Annual report pursuant to Section 13 and 15(d)

Income Taxes - Additional Information (Detail)

v3.6.0.2
Income Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Tax Disclosure [Abstract]      
Unrecognized tax benefits that would affect our effective tax rate if recognized $ 1,000,000 $ 900,000 $ 1,800,000
Decrease in unrecognized tax benefits due to lapse of statute of limitations 0 831,000 0
Increase in unrecognized tax benefits 105,000   676,000
Decrease in unrecognized tax benefits related to non-qualified stock option 0 0 165,000
Accrued interest on uncertain tax benefits 33,000 20,000 52,000
Accrued interest related to uncertain tax positions, net of federal tax benefit 101,000 67,000 366,000
Income tax deductions due to excess tax benefits 614,000    
Increase in deferred tax assets, allowance for loan losses and net operating loss carryforwards 1,000,000    
Valuation allowance 1,031,000 0 $ 0
Operating Loss Carryforwards [Line Items]      
Federal alternative minimum tax credit 400,000    
Federal [Member]      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards 5,200,000    
Low income housing tax credit 2,800,000    
State [Member]      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards 236,600,000    
Low income housing tax credit 440,000    
Central Bancorp, Inc [Member]      
Operating Loss Carryforwards [Line Items]      
Increase in deferred tax assets $ 5,800,000 $ 18,100,000