Annual report pursuant to Section 13 and 15(d)

Acquisition - Additional Information (Detail)

v3.3.1.900
Acquisition - Additional Information (Detail)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Aug. 31, 2014
USD ($)
$ / shares
Jun. 30, 2014
USD ($)
Sep. 30, 2015
USD ($)
Dec. 31, 2015
USD ($)
Branches
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Business Acquisition [Line Items]            
Bargain purchase gain     $ 14,600 $ 0 $ 14,577 $ 0
Merger and integration expense       $ 1,971 6,646 $ 730
Central Bancorp, Inc [Member]            
Business Acquisition [Line Items]            
Common stock, price per share after acquisition (in usd per share) | $ / shares $ 17.64          
Consideration paid $ 50,000          
Consideration paid for redemption of preferred stock 28,675          
Total assets acquired 1,267,921          
Total liabilities assumed 1,174,669          
Total identifiable net assets 93,252          
Loans 297,272          
Total deposits 1,098,997          
Number of branch locations | Branches       23    
Bargain purchase gain 14,577 $ 14,600        
Merger and integration expense       $ 2,000 6,600  
Core deposit intangible $ 2,213          
Core deposit intangible, useful life 10 years          
Amortization expense of core deposit intangible       133 379  
Certificates of deposit $ 11,300          
Amortization of certificates of deposit       5,600 2,300  
Discount on subordinated debentures $ 8,300          
Amortization of subordinated debentures       $ 176 $ 71