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	$ 28,613	$ 46,327	$ 52,135	$ 130,928
Other comprehensive income:
Unrealized gain (loss) on debt securities for which credit losses has been recognized	649	(557)	(16)	(488)
Reclassification adjustment for provision for credit loss expense	0	497	1,631	497
Reclassification adjustment for net gain included in net income on sales of available-for-sale securities with no credit losses previously recognized	(5,288)	0	(13,380)	0
All other unrealized holding (losses) gains on available-for-sale securities	(3,304)	7,622	50,328	45,530
Other comprehensive (loss) income for the period	(7,943)	7,562	38,563	45,539
Total comprehensive income	$ 20,670	$ 53,889	$ 90,698	$ 176,467