Other Borrowings - Additional Information (Detail) - USD ($)	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Debt Disclosure [Abstract]
Outstanding borrowings	$ 39,000,000	$ 78,881,000	$ 100,293,000
Borrowing available with FHLB	297,500,000
Credit arrangements for federal funds purchase	65,000,000
Loans pledged at federal reserve discount window	633,100,000
Loans pledged at federal reserve discount window available for borrowing	$ 441,600,000