Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 36,187	$ 30,341
Other comprehensive income (loss), net of tax:
Net gains arising during the period	8,283	3,936
Less reclassification adjustment for net gains included in net income	(170)	(1,409)
Total	8,113	2,527
Non-credit impairment losses on available for sale securities
Net change in non-credit impairment losses on securities	(59)	(421)
Less reclassification adjustment for accretion of credit impairment losses included in net income	(286)	(84)
Total	(345)	(505)
Unrealized gains and losses on derivatives (cash flow hedges)
Net losses on derivatives arising during the period	(6,552)	(5,259)
Less reclassification adjustment for net losses included in net income	1,741	951
Total	(4,811)	(4,308)
Defined benefit pension plan
Amortization of net loss	43	119
Total other comprehensive income (loss)	3,000	(2,167)
Total comprehensive income	$ 39,187	$ 28,174