Annual report pursuant to Section 13 and 15(d)

Income Taxes - Additional Information (Detail)

v3.8.0.1
Income Taxes - Additional Information (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Tax Disclosure [Abstract]      
Unrecognized tax benefits that would affect our effective tax rate if recognized $ 1,000 $ 1,000 $ 900
Decrease in unrecognized tax benefits due to lapse of statute of limitations 0 0 831
Increase in unrecognized tax benefits 105    
Accrued interest on uncertain tax benefits 34 33 20
Accrued interest related to uncertain tax positions, net of federal tax benefit 132 101 67
Income tax deductions due to excess tax benefits 1,800 614  
Increase in deferred tax assets, allowance for loan losses and net operating loss carryforwards 1,000    
Valuation allowance 2,750 1,031 $ 0
Provisional decrease to deferred tax assets and liabilities 3,900    
Net adjustment to deferred income tax expense 3,900    
Federal [Member]      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards 223,000    
Low income housing tax credit 1,000    
State [Member]      
Operating Loss Carryforwards [Line Items]      
Low income housing tax credit 200    
Central Bancorp, Inc [Member]      
Operating Loss Carryforwards [Line Items]      
Increase in deferred tax assets $ 13,900 $ 5,800