Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 161,907	$ 168,146	$ 102,957
Other comprehensive income (loss), net of tax:
Net losses arising during the period	352	(4,293)	(2,000)
Less reclassification adjustment for net losses (gains) included in net income	11	(465)	(1,446)
Total	363	(4,758)	(3,446)
Non-credit impairment losses on available for sale and held to maturity securities
Net change in non-credit impairment losses on securities	498	417	(241)
Less reclassification adjustment for accretion of credit impairment losses included in net income	(167)	(539)	(424)
Total	331	(122)	(665)
Unrealized gains and losses on derivatives (cash flow hedges)
Net losses on derivatives arising during the period	576	(2,461)	(7,239)
Less reclassification adjustment for net losses included in net income	5,028	7,641	4,127
Total	5,604	5,180	(3,112)
Defined benefit pension plan
Net (losses) gains arising during the period	(2,722)	3,298	3,444
Amortization of prior service cost	191	(181)	117
Amortization of net loss	248	185	462
Total	(2,283)	3,302	4,023
Total other comprehensive income (loss)	4,015	3,602	(3,200)
Total comprehensive income	$ 165,922	$ 171,748	$ 99,757