Federal Home Loan Bank Advances and Borrowings - Additional Information (Detail) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]    
Pledged under blanket floating liens $ 471,481,000 $ 409,911,000
Federal Home Loan Bank Advances [Member]    
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]    
Outstanding unfunded standby letters of credit 98,345,000  
Additional borrowing capacity under its borrowing arrangement with the FHLB 111,032,000  
Available lines of credit for overnight borrowings $ 84,600,000