Other Comprehensive Income (Loss) - Summary of Each Component of Accumulated Other Comprehensive Income (Loss), Net Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Jan. 11, 2013
Amounts Reclassified Out Of Accumulated Other Comprehensive Income Loss [Abstract]
Unrealized gains/losses on Available for Sale Securities, Beginning Balance	$ (43,364)		$ 5,082
Other comprehensive income (loss) before reclassification, Unrealized gains/losses on Available for Sale Securities	12,571	(2,242)
Amounts reclassified from accumulated other comprehensive income, Unrealized gains/losses on Available for Sale Securities	(3)	(721)
Unrealized gains (losses) on securities available for sale, Current Period Change	12,568	(2,963)
Unrealized gains/losses on Available for Sale Securities, Ending Balance	(30,796)	2,119	5,082
Postretirement Benefits, Beginning Balance	1,699		1,600
Other comprehensive income (loss) before reclassification, Postretirement Benefits
Amounts reclassified from accumulated other comprehensive income (loss), Postretirement Benefits
Net current period other comprehensive income (loss), Postretirement Benefits
Postretirement Benefits, Ending Balance	1,699	1,600	1,600
Total, Beginning Balance	(41,665)		6,682
Other comprehensive income (loss) before reclassification, Total	12,571	(2,242)
Amounts reclassified from accumulated other comprehensive income (loss), Total	(3)	(721)
Total other comprehensive income (loss)	12,568	(2,963)
Total, Ending Balance	$ (29,097)	$ 3,719	$ 6,682