CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 39,649	$ 42,842	$ 135,809	$ 118,056
Unrealized gains and losses on available for sale securities
Net gains arising during the period	1,457	4,902	4,660	12,550
Less reclassification adjustment for net (gains) losses included in net income	(4)	6	(4)	(162)
Total	1,453	4,908	4,656	12,388
Non-credit impairment losses on available for sale securities
Net change in non-credit impairment losses on securities	(223)	(74)	(89)	168
Less reclassification adjustment for accretion of credit impairment losses included in net income	(40)	(50)	(166)	(336)
Total	(263)	(124)	(255)	(168)
Unrealized gains and losses on derivatives (cash flow hedges)
Net gains (losses) on derivatives arising during the period	198	1,735	(548)	(6,939)
Less reclassification adjustment for net losses included in net income	1,132	2,095	3,963	5,943
Total	1,330	3,830	3,415	(996)
Defined benefit pension plan
Amortization of net loss	59	42	177	128
Total other comprehensive income	2,579	8,656	7,993	11,352
Total comprehensive income	$ 42,228	$ 51,498	$ 143,802	$ 129,408