Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 67,807	$ 83,878	$ 235,248	$ 227,530
Other comprehensive income/loss before income taxes:
Net change in unrealized gain/loss on securities available for sale and cash flow hedges	34,159	(25,242)	160,627	(110,895)
Reclassification of net losses realized and included in earnings	3,280	2,547	11,483	6,560
Other valuation adjustments for employee benefit plan	(7,015)		(7,015)	(9,039)
Amortization of unrealized net loss on securities transferred to held to maturity	954	747	2,435	2,427
Other comprehensive income/loss before income taxes	31,378	(21,948)	167,530	(110,947)
Income tax expense (benefit)	7,331	(4,978)	37,977	(25,170)
Other comprehensive income/loss net of income taxes	24,047	(16,970)	129,553	(85,777)
Comprehensive income	$ 91,854	$ 66,908	$ 364,801	$ 141,753