Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 83,878	$ 58,902	$ 227,530	$ 160,183
Other comprehensive income/loss before income taxes:
Net change in unrealized gain/loss on securities available for sale and cash flow hedges	(25,242)	5,949	(110,895)	19,794
Reclassification of net losses realized and included in earnings	2,547	1,374	6,560	4,479
Valuation adjustment for pension plan amendment				17,315
Other valuation adjustments for employee benefit plans		1,597	(9,039)	(9,185)
Amortization of unrealized net loss on securities transferred to held to maturity	747	977	2,427	2,726
Other comprehensive income/loss before income taxes	(21,948)	9,897	(110,947)	35,129
Income tax expense (benefit)	(4,978)	3,609	(25,170)	12,748
Other comprehensive income/loss net of income taxes	(16,970)	6,288	(85,777)	22,381
Comprehensive income	$ 66,908	$ 65,190	$ 141,753	$ 182,564