Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 327,380	$ 323,770	$ 215,632
Other comprehensive income (loss) before income taxes:
Net change in unrealized gain/loss on available for sale securities and cash flow hedges	143,922	(52,757)	(425)
Reclassification of net losses realized and included in earnings	13,429	34,966	5,801
Valuation adjustment for pension plan amendment			17,315
Other valuation adjustments of employee benefit plans	2,398	(45,198)	(10,929)
Amortization of unrealized net loss on securities transferred to held to maturity	3,153	3,296	3,786
Other comprehensive income (loss) before income taxes	162,902	(59,693)	15,548
Income tax expense (benefit)	36,917	(13,386)	4,088
Other comprehensive income (loss) net of income taxes	125,985	(46,307)	11,460
Comprehensive income	$ 453,365	$ 277,463	$ 227,092