Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (2,300)	$ (9,123)
Unrealized gains (losses) on investments, net of tax of $1,397 and ($1,555) in 2019 and 2018, respectively	3,657	(3,964)
Comprehensive income (loss)	$ 1,357	$ (13,087)