Other Comprehensive Income - Schedule of Changes in Accumulated Other Comprehensive Loss after Tax (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 2,207,091	$ 1,863,017	$ 1,541,040
Other comprehensive (loss) income before reclassifications	(3,039)	(6,036)	(7,622)
Amounts reclassified from other comprehensive (loss) income	6,641	2,836	3,379
Other comprehensive (loss) income, net	3,602	(3,200)	(4,243)
Ending balance	2,377,156	2,207,091	1,863,017
Unrealized Gains and Losses on AFS Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,336)	(1,890)	(20,855)
Other comprehensive (loss) income before reclassifications	(4,293)	(2,000)	19,398
Amounts reclassified from other comprehensive (loss) income	(465)	(1,446)	(433)
Other comprehensive (loss) income, net	(4,758)	(3,446)	18,965
Ending balance	(10,094)	(5,336)	(1,890)
Non-credit Impairment Losses on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(520)	145	(806)
Other comprehensive (loss) income before reclassifications	417	(241)	1,334
Amounts reclassified from other comprehensive (loss) income	(539)	(424)	(383)
Other comprehensive (loss) income, net	(122)	(665)	951
Ending balance	(642)	(520)	145
Unrealized Gains and Losses on Derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(17,644)	(14,532)	(6,271)
Other comprehensive (loss) income before reclassifications	(2,461)	(7,239)	(12,147)
Amounts reclassified from other comprehensive (loss) income	7,641	4,127	3,886
Other comprehensive (loss) income, net	5,180	(3,112)	(8,261)
Ending balance	(12,464)	(17,644)	(14,532)
Defined Benefit Pension Plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(22,195)	(26,218)	(10,320)
Other comprehensive (loss) income before reclassifications	3,298	3,444	(16,207)
Amounts reclassified from other comprehensive (loss) income	4	579	309
Other comprehensive (loss) income, net	3,302	4,023	(15,898)
Ending balance	(18,893)	(22,195)	(26,218)
Total Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(45,695)	(42,495)	(38,252)
Ending balance	$ (42,093)	$ (45,695)	$ (42,495)