Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Estimated Fair Values of Financial Instruments (Detail)

v3.3.0.814
Fair Value Measurements - Estimated Fair Values of Financial Instruments (Detail) - USD ($)
$ in Thousands
Sep. 30, 2015
Dec. 31, 2014
Dec. 31, 2013
Financial assets:      
Cash and due from banks $ 235,342 $ 158,320  
Securities available for sale 669,340 1,060,717  
Accrued interest receivable 8,722 9,749  
Investment in FRB stock 14,098 12,273  
Financial liabilities:      
Noninterest-bearing deposits 1,114,621 1,022,972  
Interest-bearing deposits 2,404,073 2,533,774  
Accrued interest payable 2,985 3,450  
Carrying Amount [Member]      
Financial assets:      
Cash and due from banks 235,342 158,320  
Securities available for sale 669,340 1,060,717  
Loans receivable, net of allowance for loan losses 2,998,712 2,735,832  
Loans held for sale 4,871 5,451  
Accrued interest receivable 8,722 9,749  
Servicing assets 11,986 13,773  
Investment in FHLB stock 16,385 17,580  
Investment in FRB stock 14,098 12,273  
Financial liabilities:      
Noninterest-bearing deposits 1,114,621 1,022,972  
Interest-bearing deposits 2,404,073 2,533,774  
Servicing liabilities 5,176 5,971  
Borrowings 168,669 168,544  
Accrued interest payable 2,985 3,450  
Off-balance sheet items:      
Commitments to extend credit 314,303 309,584  
Standby letters of credit 5,603 8,982  
Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]      
Financial assets:      
Cash and due from banks 235,342 158,320  
Securities available for sale 23,169 23,056  
Loans receivable, net of allowance for loan losses 0 0  
Loans held for sale 0 0  
Accrued interest receivable 8,722 9,749  
Servicing assets 0 0  
Investment in FHLB stock 0 0  
Investment in FRB stock 0 0  
Financial liabilities:      
Noninterest-bearing deposits 0 0  
Interest-bearing deposits 0 0  
Servicing liabilities 0 0  
Borrowings 0 0  
Accrued interest payable 2,985 3,450  
Off-balance sheet items:      
Commitments to extend credit 0 0  
Standby letters of credit 0 0  
Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]      
Financial assets:      
Cash and due from banks 0 0  
Securities available for sale 646,171 1,036,538  
Loans receivable, net of allowance for loan losses 0 0  
Loans held for sale 4,871 5,451  
Accrued interest receivable 0 0  
Servicing assets 0 0  
Investment in FHLB stock 16,385 17,580  
Investment in FRB stock 14,098 12,273  
Financial liabilities:      
Noninterest-bearing deposits 1,114,621 1,022,972  
Interest-bearing deposits 0 0  
Servicing liabilities 0 0  
Borrowings 0 0  
Accrued interest payable 0 0  
Off-balance sheet items:      
Commitments to extend credit 0 0  
Standby letters of credit 0 0  
Fair Value [Member] | Fair Value, Inputs, Level 3 [Member]      
Financial assets:      
Cash and due from banks 0 0  
Securities available for sale 0 1,123  
Loans receivable, net of allowance for loan losses 3,006,747 2,738,401  
Loans held for sale 0 0  
Accrued interest receivable 0 0  
Servicing assets 11,986 13,773  
Investment in FHLB stock 0 0  
Investment in FRB stock 0 0  
Financial liabilities:      
Noninterest-bearing deposits 0 0  
Interest-bearing deposits 2,404,110 2,528,304  
Servicing liabilities 5,176 5,971  
Borrowings 168,669 149,983  
Accrued interest payable 0 0  
Off-balance sheet items:      
Commitments to extend credit 314,303 309,584  
Standby letters of credit 5,603 8,982  
U.S. government agency securities [Member]      
Financial assets:      
Securities available for sale 57,674 128,207  
U.S. government agency securities [Member] | Carrying Amount [Member]      
Off-balance sheet items:      
Fair value reclassification from Level 1 to Level 2   128,200  
U.S. government agency securities [Member] | Carrying Amount [Member] | Fair Value, Inputs, Level 1 [Member]      
Financial assets:      
Securities available for sale     $ 128,400
U.S. government agency securities [Member] | Carrying Amount [Member] | Fair Value, Inputs, Level 2 [Member]      
Financial assets:      
Securities available for sale     $ 931,200
Other securities [Member]      
Financial assets:      
Securities available for sale $ 23,007 22,893  
Other securities [Member] | Carrying Amount [Member]      
Off-balance sheet items:      
Fair value reclassification from Level 2 to Level 1   $ 22,900