Other Comprehensive Income (Loss) - Summary of Accumulated Other Comprehensive Income (Loss) Balances, Net of Tax (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Equity [Abstract]
Unrealized gains (losses) on securities available for sale, Beginning Balance			$ (43,364)	$ 5,082
Unrealized gains (losses) on post-retirement benefits, Beginning Balance			1,699	1,600
Total, Beginning Balance			(41,665)	6,682
Unrealized gains (losses) on securities available for sale, Current Period Change	(409)	(2,121)	15,355	(38,006)
Total, Current Period Change	(409)	(2,121)	15,355	(38,006)
Unrealized gains (losses) on securities available for sale, Ending Balance	(28,009)	(32,924)	(28,009)	(32,924)
Unrealized gains (losses) on post-retirement benefits, Ending Balance	1,699	1,600	1,699	1,600
Total, Ending Balance	$ (26,310)	$ (31,324)	$ (26,310)	$ (31,324)