Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 38,062	$ 25,170	$ 18,799
Unrealized (losses) gains on investments, net of tax	(3,638)	(1,427)	28
Comprehensive income	$ 34,424	$ 23,743	$ 18,827