Other Comprehensive Income (Loss) - Components of Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive (loss) income, Before Tax	$ 9,037	$ (21,320)	$ 15,594	$ (24,130)
Total other comprehensive (loss) income, Tax Effect	(3,378)	8,710	(6,057)	9,857
Total other comprehensive income (loss)	5,659	(12,610)	9,537	(14,273)
Unrealized gains on securities available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net (losses) gains, Before Tax	10,188	(21,239)	16,475	(23,977)
Reclassification adjustment, Before Tax	(110)	(423)	240	(934)
Total other comprehensive (loss) income, Before Tax	10,078	(21,662)	16,715	(24,911)
Net (losses) gains, Tax Effect	(3,849)	8,677	(6,417)	9,795
Reclassification adjustment, Tax Effect	(45)	(173)	98	(382)
Total other comprehensive (loss) income, Tax Effect	(3,804)	8,850	(6,515)	10,177
Net (losses) gains, After Tax	6,339	(12,562)	10,058	(14,182)
Reclassification adjustment, After Tax	(65)	(250)	142	(552)
Total other comprehensive income (loss)	6,274	(12,812)	10,200	(14,734)
Post-retirement obligations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive (loss) income, Before Tax	(1,041)	342	(1,121)	781
Total other comprehensive (loss) income, Tax Effect	426	(140)	458	(320)
Total other comprehensive income (loss)	$ (615)	$ 202	$ (663)	$ 461