CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 69,559	$ 39,649	$ 184,326	$ 135,809
Unrealized gains and losses on available for sale securities
Net (losses) gains arising during the period	(8,675)	1,457	(36,065)	4,660
Less reclassification adjustment for net losses (gains) included in net income	52	(4)	630	(4)
Total	(8,623)	1,453	(35,435)	4,656
Non-credit impairment losses on available for sale securities
Net change in non-credit impairment losses on securities	(8)	(223)	(64)	(89)
Less reclassification adjustment for accretion of credit impairment losses included in net income	5	(40)	1	(166)
Total	(3)	(263)	(63)	(255)
Unrealized gains and losses on derivatives (cash flow hedges)
Net gains (losses) on derivatives arising during the period	221	198	2,636	(548)
Less reclassification adjustment for net losses included in net income	472	1,132	2,127	3,963
Total	693	1,330	4,763	3,415
Defined benefit pension plan
Amortization of net loss	113	59	337	177
Total other comprehensive (loss) income	(7,820)	2,579	(30,398)	7,993
Total comprehensive income	$ 61,739	$ 42,228	$ 153,928	$ 143,802