Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 168,146	$ 102,957	$ 116,172
Other comprehensive income (loss), net of tax:
Net (losses) gains arising during the period	(4,293)	(2,000)	19,398
Less reclassification adjustment for net gains included in net income	(465)	(1,446)	(433)
Total	(4,758)	(3,446)	18,965
Non-credit impairment losses on available for sale and held to maturity securities
Net change in non-credit impairment losses on securities	417	(241)	1,334
Less reclassification adjustment for accretion of credit impairment losses included in net income	(539)	(424)	(383)
Total	(122)	(665)	951
Unrealized gains and losses on derivatives (cash flow hedges)
Net losses on derivatives arising during the period	(2,461)	(7,239)	(12,147)
Less reclassification adjustment for net losses included in net income	7,641	4,127	3,886
Total	5,180	(3,112)	(8,261)
Defined benefit pension plan
Net gains (losses) arising during the period	3,298	3,444	(16,207)
Amortization of prior service cost	(181)	117	177
Amortization of net loss	185	462	132
Total	3,302	4,023	(15,898)
Total other comprehensive income (loss)	3,602	(3,200)	(4,243)
Total comprehensive income	$ 171,748	$ 99,757	$ 111,929