Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 88,718	$ (117,072)	$ 195,890	$ (228,105)
Other comprehensive income (loss) before income taxes:
Net change in unrealized gain or loss on securities available for sale and cash flow hedges	50,135	51,532	(95,355)	216,829
Reclassification of net loss realized and included in earnings	(3,198)	(2,885)	(2,912)	(2,517)
Valuation adjustments to pension plan attributable to the Voluntary Early Retirement Program (VERIP) and curtailment	59,606		59,606
Other valuation adjustments to employee benefit plans	(10,651)	(10,251)	(10,651)	(10,251)
Amortization of unrealized net loss or gain on securities transferred to held to maturity	(45)	(94)	(101)	(289)
Other comprehensive income (loss) before income taxes	95,847	38,302	(49,413)	203,772
Income tax expense (benefit)	21,542	8,842	(12,206)	46,322
Other comprehensive income (loss) net of income taxes	74,305	29,460	(37,207)	157,450
Comprehensive income (loss)	$ 163,023	$ (87,612)	$ 158,683	$ (70,655)