Annual report pursuant to Section 13 and 15(d)

Accounting for Investments in Qualified Affordable Housing Projects - Summary of Change in Accounting Principle on Statements of Income (Detail)

v2.4.1.9
Accounting for Investments in Qualified Affordable Housing Projects - Summary of Change in Accounting Principle on Statements of Income (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Interest and dividend income $ 41,462us-gaap_InterestAndDividendIncomeOperating $ 34,562us-gaap_InterestAndDividendIncomeOperating $ 30,343us-gaap_InterestAndDividendIncomeOperating $ 30,367us-gaap_InterestAndDividendIncomeOperating $ 30,088us-gaap_InterestAndDividendIncomeOperating $ 30,807us-gaap_InterestAndDividendIncomeOperating $ 29,598us-gaap_InterestAndDividendIncomeOperating $ 28,647us-gaap_InterestAndDividendIncomeOperating $ 136,734us-gaap_InterestAndDividendIncomeOperating $ 119,140us-gaap_InterestAndDividendIncomeOperating $ 117,282us-gaap_InterestAndDividendIncomeOperating
Interest expense 4,106us-gaap_InterestExpense 3,475us-gaap_InterestExpense 3,183us-gaap_InterestExpense 3,269us-gaap_InterestExpense 3,338us-gaap_InterestExpense 3,153us-gaap_InterestExpense 3,225us-gaap_InterestExpense 3,791us-gaap_InterestExpense 14,033us-gaap_InterestExpense 13,507us-gaap_InterestExpense 18,745us-gaap_InterestExpense
Provision for credit losses 1,026us-gaap_ProvisionForLoanLeaseAndOtherLosses   (3,866)us-gaap_ProvisionForLoanLeaseAndOtherLosses (3,300)us-gaap_ProvisionForLoanLeaseAndOtherLosses         (6,140)us-gaap_ProvisionForLoanLeaseAndOtherLosses   6,000us-gaap_ProvisionForLoanLeaseAndOtherLosses
Net interest income before provision for credit losses 37,356us-gaap_InterestIncomeExpenseNet 31,087us-gaap_InterestIncomeExpenseNet 27,160us-gaap_InterestIncomeExpenseNet 27,098us-gaap_InterestIncomeExpenseNet 26,750us-gaap_InterestIncomeExpenseNet 27,654us-gaap_InterestIncomeExpenseNet 26,373us-gaap_InterestIncomeExpenseNet 24,856us-gaap_InterestIncomeExpenseNet 122,701us-gaap_InterestIncomeExpenseNet 105,633us-gaap_InterestIncomeExpenseNet 98,537us-gaap_InterestIncomeExpenseNet
Noninterest income 8,984us-gaap_NoninterestIncome 21,611us-gaap_NoninterestIncome 5,487us-gaap_NoninterestIncome 6,214us-gaap_NoninterestIncome 6,765us-gaap_NoninterestIncome 6,464us-gaap_NoninterestIncome 7,103us-gaap_NoninterestIncome 7,568us-gaap_NoninterestIncome 42,296us-gaap_NoninterestIncome 27,900us-gaap_NoninterestIncome 21,413us-gaap_NoninterestIncome
Noninterest expense 37,085us-gaap_NoninterestExpense 25,530us-gaap_NoninterestExpense 18,138us-gaap_NoninterestExpense 17,800us-gaap_NoninterestExpense 18,278us-gaap_NoninterestExpense 17,221us-gaap_NoninterestExpense 18,191us-gaap_NoninterestExpense 17,327us-gaap_NoninterestExpense 98,553us-gaap_NoninterestExpense 71,017us-gaap_NoninterestExpense 70,611us-gaap_NoninterestExpense
Income from continuing operations before provision for income taxes                 72,584us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest 62,516us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest 43,339us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
(Benefit) provision for income taxes 2,301us-gaap_IncomeTaxExpenseBenefit 5,368us-gaap_IncomeTaxExpenseBenefit 6,866us-gaap_IncomeTaxExpenseBenefit 7,844us-gaap_IncomeTaxExpenseBenefit 5,222us-gaap_IncomeTaxExpenseBenefit 6,582us-gaap_IncomeTaxExpenseBenefit 5,958us-gaap_IncomeTaxExpenseBenefit 4,970us-gaap_IncomeTaxExpenseBenefit 22,379us-gaap_IncomeTaxExpenseBenefit 22,732us-gaap_IncomeTaxExpenseBenefit (46,818)us-gaap_IncomeTaxExpenseBenefit
Income from continuing operations 5,928us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest 21,800us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest 11,509us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest 10,968us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest 10,015us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest 10,315us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest 9,327us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest 10,127us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest 50,205us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest 39,784us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest 90,157us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest
Earnings per share from continuing operations                      
Basic $ 0.19us-gaap_IncomeLossFromContinuingOperationsPerBasicShare $ 0.69us-gaap_IncomeLossFromContinuingOperationsPerBasicShare $ 0.36us-gaap_IncomeLossFromContinuingOperationsPerBasicShare $ 0.34us-gaap_IncomeLossFromContinuingOperationsPerBasicShare $ 0.31us-gaap_IncomeLossFromContinuingOperationsPerBasicShare $ 0.33us-gaap_IncomeLossFromContinuingOperationsPerBasicShare $ 0.30us-gaap_IncomeLossFromContinuingOperationsPerBasicShare $ 0.32us-gaap_IncomeLossFromContinuingOperationsPerBasicShare $ 1.58us-gaap_IncomeLossFromContinuingOperationsPerBasicShare $ 1.26us-gaap_IncomeLossFromContinuingOperationsPerBasicShare $ 2.86us-gaap_IncomeLossFromContinuingOperationsPerBasicShare
Diluted $ 0.19us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare $ 0.68us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare $ 0.36us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare $ 0.34us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare $ 0.31us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare $ 0.33us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare $ 0.29us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare $ 0.33us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare $ 1.57us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare $ 1.26us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare $ 2.86us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare
As Previously Reported [Member]                      
Interest and dividend income                   119,140us-gaap_InterestAndDividendIncomeOperating
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
117,282us-gaap_InterestAndDividendIncomeOperating
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
Interest expense                   13,507us-gaap_InterestExpense
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
18,745us-gaap_InterestExpense
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
Provision for credit losses                     6,000us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
Net interest income before provision for credit losses                   105,633us-gaap_InterestIncomeExpenseNet
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
92,537us-gaap_InterestIncomeExpenseNet
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
Noninterest income                   27,900us-gaap_NoninterestIncome
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
21,413us-gaap_NoninterestIncome
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
Noninterest expense                   71,656us-gaap_NoninterestExpense
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
71,231us-gaap_NoninterestExpense
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
Income from continuing operations before provision for income taxes                   61,877us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
42,719us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
(Benefit) provision for income taxes                   22,044us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
(47,488)us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
Income from continuing operations                   39,833us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
90,207us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
Earnings per share from continuing operations                      
Basic                   $ 1.26us-gaap_IncomeLossFromContinuingOperationsPerBasicShare
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
$ 2.87us-gaap_IncomeLossFromContinuingOperationsPerBasicShare
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
Diluted                   $ 1.26us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
$ 2.86us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
Effect of Change in Accounting Principle [Member]                      
Noninterest expense                   (639)us-gaap_NoninterestExpense
/ us-gaap_StatementScenarioAxis
= us-gaap_RestatementAdjustmentMember
(620)us-gaap_NoninterestExpense
/ us-gaap_StatementScenarioAxis
= us-gaap_RestatementAdjustmentMember
Income from continuing operations before provision for income taxes                   639us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
/ us-gaap_StatementScenarioAxis
= us-gaap_RestatementAdjustmentMember
620us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
/ us-gaap_StatementScenarioAxis
= us-gaap_RestatementAdjustmentMember
(Benefit) provision for income taxes                   688us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_StatementScenarioAxis
= us-gaap_RestatementAdjustmentMember
670us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_StatementScenarioAxis
= us-gaap_RestatementAdjustmentMember
Income from continuing operations                   $ (49)us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest
/ us-gaap_StatementScenarioAxis
= us-gaap_RestatementAdjustmentMember
$ (50)us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest
/ us-gaap_StatementScenarioAxis
= us-gaap_RestatementAdjustmentMember
Earnings per share from continuing operations                      
Basic                     $ (0.01)us-gaap_IncomeLossFromContinuingOperationsPerBasicShare
/ us-gaap_StatementScenarioAxis
= us-gaap_RestatementAdjustmentMember