Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 28,501	$ 23,353	$ 23,948	$ 10,800	$ 34,014	$ 21,386	$ 17,890	$ 19,400	$ 86,602	$ 92,690	$ 71,632
Other comprehensive income:
Unrealized gain (loss) on debt securities, net of tax									8,808	13,043	(4,243)
Comprehensive income	$ 29,608	$ 24,087	$ 29,431	$ 12,284	$ 33,610	$ 23,862	$ 23,068	$ 25,193	$ 95,410	$ 105,733	$ 67,389