Accumulated Other Comprehensive Loss - Schedule of Changes in Accumulated Other Comprehensive Loss After Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance			$ (42,495)
Total other comprehensive (loss) income	$ (792)	$ 1,910	(6,557)	$ 9,865
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(49,052)		(49,052)
Unrealized Gains and (Losses) on Available for Sale (AFS) Securities
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(5,153)		(1,890)
Other comprehensive income (loss) before reclassifications	4,586		2,677
Amounts reclassified from other comprehensive income (loss)	(91)		(1,445)
Total other comprehensive (loss) income	4,495		1,232
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(658)		(658)
Non-credit Impairment Losses on AFS Securities
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(411)		145
Other comprehensive income (loss) before reclassifications	252		(200)
Amounts reclassified from other comprehensive income (loss)	(267)		(371)
Total other comprehensive (loss) income	(15)		(571)
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(426)		(426)
Unrealized Gains and (Losses) on Derivatives
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(16,718)		(14,532)
Other comprehensive income (loss) before reclassifications	(6,163)		(10,291)
Amounts reclassified from other comprehensive income (loss)	772		2,714
Total other comprehensive (loss) income	(5,391)		(7,577)
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(22,109)		(22,109)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(48,260)		(42,495)
Other comprehensive income (loss) before reclassifications	(1,325)		(7,814)
Amounts reclassified from other comprehensive income (loss)	533		1,257
Total other comprehensive (loss) income	(792)		(6,557)
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(49,052)		(49,052)
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(25,978)		(26,218)
Other comprehensive income (loss) before reclassifications	0		0
Amounts reclassified from other comprehensive income (loss)	119		359
Total other comprehensive (loss) income	119		359
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (25,859)		$ (25,859)