Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 46,095	$ 36,187
Unrealized gains and losses on available for sale securities
Net gains arising during the period	1,307	8,283
Less reclassification adjustment for net losses (gains) included in net income	13	(170)
Total	1,320	8,113
Non-credit impairment losses on available for sale securities
Net change in non-credit impairment losses on securities	113	(59)
Less reclassification adjustment for accretion of credit impairment losses included in net income	(87)	(286)
Total	26	(345)
Unrealized gains and losses on derivatives (cash flow hedges)
Net gains (losses) on derivatives arising during the period	127	(6,552)
Less reclassification adjustment for net losses included in net income	1,475	1,741
Total	1,602	(4,811)
Defined benefit pension plan
Amortization of net loss	59	43
Total other comprehensive income	3,007	3,000
Total comprehensive income	$ 49,102	$ 39,187