Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (117,072)	$ 88,277	$ (228,105)	$ 167,441
Other comprehensive income before income taxes:
Net change in unrealized gain or loss on securities available for sale and cash flow hedges	51,532	69,225	216,829	126,468
Reclassification of net gain or loss realized and included in earnings	(2,885)	3,984	(2,517)	8,203
Valuation adjustments to employee benefit plan	(10,251)		(10,251)
Amortization of unrealized net loss or gain on securities transferred to held to maturity	(94)	890	(289)	1,481
Other comprehensive income before income taxes	38,302	74,099	203,772	136,152
Income tax expense	8,842	16,793	46,322	30,646
Other comprehensive income net of income taxes	29,460	57,306	157,450	105,506
Comprehensive income (loss)	$ (87,612)	$ 145,583	$ (70,655)	$ 272,947