CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 72,802	$ 50,065	$ 114,767	$ 96,160
Unrealized gains and losses on available for sale securities
Net (losses) gains arising during the period	(6,461)	1,896	(27,390)	3,203
Less reclassification adjustment for net losses (gains) included in net income	30	(13)	578	0
Total	(6,431)	1,883	(26,812)	3,203
Non-credit impairment losses on available for sale securities
Net change in non-credit impairment losses on securities	212	21	(56)	134
Less reclassification adjustment for accretion of credit impairment losses included in net income	12	(39)	(4)	(126)
Total	224	(18)	(60)	8
Unrealized gains and losses on derivatives (cash flow hedges)
Net gains (losses) on derivatives arising during the period	455	(873)	2,415	(746)
Less reclassification adjustment for net losses included in net income	619	1,356	1,655	2,831
Total	1,074	483	4,070	2,085
Defined benefit pension plan
Amortization of net loss	112	59	224	118
Total other comprehensive (loss) income	(5,021)	2,407	(22,578)	5,414
Total comprehensive income	$ 67,781	$ 52,472	$ 92,189	$ 101,574