CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 261,428	$ 161,907	$ 168,146
Other comprehensive (loss) income, net of tax:
Net (losses) gains arising during the period	(22,932)	352	(4,293)
Less reclassification adjustment for net losses (gains) included in net income	1,857	11	(465)
Total	(21,075)	363	(4,758)
Non-credit impairment losses on available for sale and held to maturity securities
Net change in non-credit impairment losses on securities	0	498	417
Less reclassification adjustment for accretion of credit impairment losses included in net income	380	(167)	(539)
Total	380	331	(122)
Unrealized gains and losses on derivatives (cash flow hedges)
Net gains (losses) on derivatives arising during the period	1,874	576	(2,461)
Less reclassification adjustment for net losses included in net income	2,494	5,028	7,641
Total	4,368	5,604	5,180
Defined benefit pension plan
Net (losses) gains arising during the period	(7,151)	(2,722)	3,298
Amortization of prior service cost	146	191	(181)
Amortization of net loss	447	248	185
Total	(6,558)	(2,283)	3,302
Total other comprehensive (loss) income	(22,885)	4,015	3,602
Total comprehensive income	$ 238,543	$ 165,922	$ 171,748