Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 52,072	$ 67,158
Unrealized gains and losses on securities:
Change in unrealized securities gains (losses) arising during period	68,033	30,415
Tax effect	(26,016)	(11,813)
Reclassification adjustment for net gains realized and included in income before income taxes	4,628	5,126
Tax effect	1,770	1,977
Total change in unrealized gains and losses on securities, net of tax	39,159	15,453
Change in fair value of cash flow hedges:
Change in unrecognized loss on cash flow hedges	700	576
Tax effect	(263)	(222)
Total change in unrecognized loss on cash flow hedges, net of tax	437	354
Change in pension obligation:
Amortization of actuarial losses and prior service cost	1,652	2,886
Tax effect	(632)	(1,123)
Total change in pension obligation, net of tax	1,020	1,763
Net current period other comprehensive income	40,616	17,570
Total comprehensive income	$ 92,688	$ 84,728