Shareholders' Equity - Summary of Each Component of Accumulated Other Comprehensive Income (Loss), Net Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Amounts Reclassified Out Of Accumulated Other Comprehensive Income Loss [Abstract]
Unrealized gains/losses on Available for Sale Securities, Beginning Balance	$ 5,082
Other comprehensive income (loss) before reclassification, Unrealized gains/losses on Available for Sale Securities	(45,869)
Amounts reclassified from accumulated other comprehensive loss, Unrealized gains/losses on Available for Sale Securities	(2,577)	(6,325)	(8,633)
Unrealized gains (losses) on securities available for sale, Current Period Change	(48,446)	1,635	9,120
Unrealized gains/losses on Available for Sale Securities, Ending Balance	(43,364)	5,082
Postretirement Benefits, Beginning Balance	1,600
Other comprehensive income (loss) before reclassification, Postretirement Benefits	288
Amounts reclassified from accumulated other comprehensive loss, Postretirement Benefits	(189)
Net current period other comprehensive loss, Postretirement Benefits	99	15	690
Postretirement Benefits, Ending Balance	1,699	1,600
Total, Beginning Balance	6,682
Other comprehensive income (loss) before reclassification, Total	(45,581)
Amounts reclassified from accumulated other comprehensive loss, Total	(2,766)
Total other comprehensive income (loss)	(48,347)	1,650	9,810
Total, Ending Balance	$ (41,665)	$ 6,682