Accumulated Other Comprehensive Income (Loss) - Schedule of AOCI (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ 1,814,417	$ 1,491,170
Other comprehensive income (loss) before reclassifications	$ (2,397)	$ 4,037	25,942	13,138
Amounts reclassified from AOCI	(680)	751	(767)	2,830
Net other comprehensive income (loss)	(3,077)	4,788	25,175	15,968
Ending Balance	1,906,823	1,834,457	1,906,823	1,834,457
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(12,457)	13,783	(39,012)	(3,806)
Other comprehensive income (loss) before reclassifications	(2,531)	2,094	26,928	21,584
Amounts reclassified from AOCI	(1,883)	(1,006)	(4,787)	(2,907)
Net other comprehensive income (loss)	(4,414)	1,088	22,141	18,677
Ending Balance	(16,871)	14,871	(16,871)	14,871
Accumulated Unrealized Gains and Losses on Held-to-Maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(12,717)	(13,867)	(13,310)	(14,480)
Amounts reclassified from AOCI	300	289	893	902
Net other comprehensive income (loss)	300	289	893	902
Ending Balance	(12,417)	(13,578)	(12,417)	(13,578)
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(5,645)	(17,184)	(6,715)	(9,276)
Other comprehensive income (loss) before reclassifications	134	1,943	(986)	(8,446)
Amounts reclassified from AOCI	887	1,156	3,077	3,637
Net other comprehensive income (loss)	1,021	3,099	2,091	(4,809)
Ending Balance	(4,624)	(14,085)	(4,624)	(14,085)
Defined Benefit Pension Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(301)	(6,349)	(335)	(7,235)
Amounts reclassified from AOCI	16	312	50	1,198
Net other comprehensive income (loss)	16	312	50	1,198
Ending Balance	(285)	(6,037)	(285)	(6,037)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(31,120)	(23,617)	(59,372)	(34,797)
Ending Balance	$ (34,197)	$ (18,829)	$ (34,197)	$ (18,829)