Accumulated Other Comprehensive Income (Loss) - Schedule of AOCI (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ 1,814,417	$ 1,491,170
Other comprehensive income (loss) before reclassifications	$ 18,012	$ 5,428	28,339	9,810
Amounts reclassified from AOCI	(567)	540	(87)	1,370
Net other comprehensive income (loss)	17,445	5,968	28,252	11,180
Ending Balance	1,886,594	1,811,117	1,886,594	1,811,117
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(29,992)	6,777	(39,012)	(3,806)
Other comprehensive income (loss) before reclassifications	19,492	8,208	29,459	19,490
Amounts reclassified from AOCI	(1,957)	(1,202)	(2,904)	(1,901)
Net other comprehensive income (loss)	17,535	7,006	26,555	17,589
Ending Balance	(12,457)	13,783	(12,457)	13,783
Accumulated Unrealized Gains and Losses on Held-to-Maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(13,015)	(14,174)	(13,310)	(14,480)
Amounts reclassified from AOCI	298	307	593	613
Net other comprehensive income (loss)	298	307	593	613
Ending Balance	(12,717)	(13,867)	(12,717)	(13,867)
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(5,240)	(15,387)	(6,715)	(9,276)
Other comprehensive income (loss) before reclassifications	(1,480)	(2,780)	(1,120)	(9,680)
Amounts reclassified from AOCI	1,075	983	2,190	1,772
Net other comprehensive income (loss)	(405)	(1,797)	1,070	(7,908)
Ending Balance	(5,645)	(17,184)	(5,645)	(17,184)
Defined Benefit Pension Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(318)	(6,801)	(335)	(7,235)
Amounts reclassified from AOCI	17	452	34	886
Net other comprehensive income (loss)	17	452	34	886
Ending Balance	(301)	(6,349)	(301)	(6,349)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(48,565)	(29,585)	(59,372)	(34,797)
Ending Balance	$ (31,120)	$ (23,617)	$ (31,120)	$ (23,617)