Quarterly report pursuant to Section 13 or 15(d)

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

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Acquisition - Business Acquisition, Unaudited Proforma Result of Operation Information (Detail) (Central Bancorp, Inc [Member], USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Central Bancorp, Inc [Member]
       
Loans At Acquisition Date [Line Items]        
Pro forma revenues (net interest income plus noninterest income) $ 62,427 $ 55,727 $ 170,923 $ 182,135
Pro forma net income from continuing operations $ 18,359 $ 12,826 $ 43,546 $ 47,201
Pro forma earnings per share from continuing operations:        
Basic $ 0.58 $ 0.41 $ 1.37 $ 1.49
Diluted $ 0.57 $ 0.40 $ 1.36 $ 1.49