Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 13,907	$ 11,240	$ 11,607	$ 2,117
Unrealized gains (losses) on investments, net of tax	3,043	(975)	6,700	(4,939)
Comprehensive income (loss)	$ 16,950	$ 10,265	$ 18,307	$ (2,822)