Securities - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2013	Jun. 30, 2015	Jun. 30, 2014
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities transferred to held-to-maturity securities			$ 536,000
Unrealized net loss on securities transferred from available-for-sale to held-to-maturity, Gross			$ 13,300
Realized gains or losses on the sale of securities	$ 0	$ 348		$ 0	$ 348
Corporate debt securities, callable, amortized cost	55,000			55,000
Corporate debt securities, callable, estimated fair value	$ 47,300			$ 47,300
Floating-rate securities, purchased period				1998
Floating-rate debt securities, fixed interest rate period				Over 90-day LIBOR
Principal maturity year				2028 or prior if called by the issuer