CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 41,965	$ 46,095
Unrealized gains and losses on available for sale securities
Net (losses) gains arising during the period	(20,929)	1,307
Less reclassification adjustment for net losses included in net income	548	13
Total	(20,381)	1,320
Non-credit impairment losses on available for sale securities
Net change in non-credit impairment losses on securities	(268)	113
Less reclassification adjustment for accretion of credit impairment losses included in net income	(16)	(87)
Total	(284)	26
Unrealized gains and losses on derivatives (cash flow hedges)
Net gains on derivatives arising during the period	1,960	127
Less reclassification adjustment for net losses included in net income	1,036	1,475
Total	2,996	1,602
Defined benefit pension plan
Amortization of net loss	112	59
Total other comprehensive (loss) income	(17,557)	3,007
Total comprehensive income	$ 24,408	$ 49,102