Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 79,356	$ 67,807	$ (148,749)	$ 235,248
Other comprehensive income (loss) before income taxes:
Net change in unrealized gain or loss on securities available for sale and cash flow hedges	425	34,159	217,254	160,627
Reclassification of net gain or loss realized and included in earnings	(4,076)	3,280	(6,593)	11,483
Valuation adjustment to employee benefit plan		(7,015)	(10,251)	(7,015)
Amortization of unrealized net loss or gain on securities transferred to held to maturity	(89)	954	(378)	2,435
Other comprehensive income (loss) before income taxes	(3,740)	31,378	200,032	167,530
Income tax expense	48	7,331	46,370	37,977
Other comprehensive income (loss) net of income taxes	(3,788)	24,047	153,662	129,553
Comprehensive income	$ 75,568	$ 91,854	$ 4,913	$ 364,801