Other Comprehensive Income (Loss) - Other Comprehensive Income (Loss) Components and Related Tax Effects (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 holding gain (loss) on securities available for sale	$ (302)	$ (2,121)	$ 23,985	$ (35,428)
Unrealized holding gain (loss) on postretirement benefits	0	0	0	0
Reclassification adjustment for gains realized in income	(328)	0	(362)	(2,578)
Net unrealized gains (losses)	(630)	(2,121)	23,623	(38,006)
Tax effect	221		(8,268)
Net of tax amount	$ (409)	$ (2,121)	$ 15,355	$ (38,006)