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	$ 21,256	$ 41,287	$ 23,522	$ 84,601
Other comprehensive income:
Unrealized (loss) gain on debt securities for which credit losses has been recognized	(537)	60	(665)	69
Reclassification adjustment for provision for credit loss expense	1,263	0	1,631	0
Reclassification adjustment for net gain (loss) included in net income on sales of available-for-sale securities with no credit losses previously recognized	155	0	(8,092)	0
All other unrealized holding gains on available-for-sale securities	3,273	17,407	53,632	37,908
Other comprehensive income (loss) for the period	4,154	17,467	46,506	37,977
Total comprehensive income	$ 25,410	$ 58,754	$ 70,028	$ 122,578