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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss)
Beginning balance			$ 2,207,091
Other comprehensive income (loss) before reclassifications	$ 6,563		5,779
Amounts reclassified from other comprehensive income (loss)	2,093	$ 533	5,573	$ 1,257
Total other comprehensive income (loss)	8,656		11,352
Ending balance	2,257,073		2,257,073
Unrealized Gains and Losses on Available for Sale (AFS) Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	2,144		(5,336)
Other comprehensive income (loss) before reclassifications	4,902		12,550
Amounts reclassified from other comprehensive income (loss)	6		(162)
Total other comprehensive income (loss)	4,908		12,388
Ending balance	7,052		7,052
Non-credit Impairment Losses on AFS Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(564)		(520)
Other comprehensive income (loss) before reclassifications	(74)		168
Amounts reclassified from other comprehensive income (loss)	(50)		(336)
Total other comprehensive income (loss)	(124)		(168)
Ending balance	(688)		(688)
Unrealized Gains and (Losses) on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(22,470)		(17,644)
Other comprehensive income (loss) before reclassifications	1,735		(6,939)
Amounts reclassified from other comprehensive income (loss)	2,095		5,943
Total other comprehensive income (loss)	3,830		(996)
Ending balance	(18,640)		(18,640)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(42,999)		(45,695)
Ending balance	(34,343)		(34,343)
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(22,109)		(22,195)
Other comprehensive income (loss) before reclassifications	0		0
Amounts reclassified from other comprehensive income (loss)	42	$ 119	128	$ 359
Total other comprehensive income (loss)	42		128
Ending balance	$ (22,067)		$ (22,067)