Annual report pursuant to Section 13 and 15(d)

Acquisition - Business Acquisition, Unaudited Proforma Result of Operation Information (Detail)

v3.3.1.900
Acquisition - Business Acquisition, Unaudited Proforma Result of Operation Information (Detail) - Central Bancorp, Inc [Member]
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2014
USD ($)
$ / shares
Business Acquisition [Line Items]  
Pro forma revenues (net interest income plus noninterest income) | $ $ 225,120
Pro forma net income from continuing operations | $ $ 56,448
Pro forma earnings per share from continuing operations:  
Basic (in usd per share) | $ / shares $ 1.78
Diluted (in usd per share) | $ / shares $ 1.77