Other Commitments and Contingencies and Derivatives - Loan Commitments Outstanding (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Loss Contingencies [Line Items]    
Total loan commitments outstanding $ 613,589 $ 439,284
Construction [Member] | Unadvanced Portion of Existing Loans [Member]
   
Loss Contingencies [Line Items]    
Total loan commitments outstanding 239,977 166,482
Construction [Member] | Commitments to Originate [Member]
   
Loss Contingencies [Line Items]    
Total loan commitments outstanding 83,439 83,078
Home Equity Line of Credit [Member] | Unadvanced Portion of Existing Loans [Member]
   
Loss Contingencies [Line Items]    
Total loan commitments outstanding 37,422 39,698
Other Lines and Letters of Credit [Member] | Unadvanced Portion of Existing Loans [Member]
   
Loss Contingencies [Line Items]    
Total loan commitments outstanding 104,956 56,174
One-to Four-Family [Member] | Commitments to Originate [Member]
   
Loss Contingencies [Line Items]    
Total loan commitments outstanding 11,592 17,752
Commercial Real Estate [Member] | Commitments to Originate [Member]
   
Loss Contingencies [Line Items]    
Total loan commitments outstanding 92,526 51,540
Commercial Business Loans [Member] | Commitments to Originate [Member]
   
Loss Contingencies [Line Items]    
Total loan commitments outstanding 39,928 24,355
Other Loans [Member] | Commitments to Originate [Member]
   
Loss Contingencies [Line Items]    
Total loan commitments outstanding $ 3,749 $ 205