Other Comprehensive Income - Schedule of Changes in Accumulated Other Comprehensive Loss after Tax (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (42,495)
Total other comprehensive (loss) income	(3,200)	$ (4,243)	$ 12,657
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(45,695)	(42,495)
Unrealized Gains and Losses on AFS Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(1,890)	(20,855)	906
Other comprehensive income (loss) before reclassifications	(2,000)	19,398	(13,239)
Amounts reclassified from other comprehensive income (loss)	(1,446)	(433)	(8,522)
Total other comprehensive (loss) income	(3,446)	18,965	(21,761)
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(5,336)	(1,890)	(20,855)
Non-Credit Impairment Losses on Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	145	(806)	(4,175)
Other comprehensive income (loss) before reclassifications	(241)	1,334	3,637
Amounts reclassified from other comprehensive income (loss)	(424)	(383)	(268)
Total other comprehensive (loss) income	(665)	951	3,369
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(520)	145	(806)
Unrealized Gains and Losses on Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(14,532)	(6,271)	(12,676)
Other comprehensive income (loss) before reclassifications	(7,239)	(12,147)	2,400
Amounts reclassified from other comprehensive income (loss)	4,127	3,886	4,005
Total other comprehensive (loss) income	(3,112)	(8,261)	6,405
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(17,644)	(14,532)	(6,271)
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(26,218)	(10,320)	(34,964)
Other comprehensive income (loss) before reclassifications	3,444	(16,207)	21,577
Amounts reclassified from other comprehensive income (loss)	579	309	3,067
Total other comprehensive (loss) income	4,023	(15,898)	24,644
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(22,195)	(26,218)	(10,320)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(42,495)	(38,252)	(50,909)
Other comprehensive income (loss) before reclassifications	(6,036)	(7,622)	14,375
Amounts reclassified from other comprehensive income (loss)	2,836	3,379	(1,718)
Total other comprehensive (loss) income	(3,200)	(4,243)	12,657
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (45,695)	$ (42,495)	$ (38,252)