Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 6,721	$ 3,728	$ 40,984	$ 16,621
Other comprehensive income (loss), net of tax:
Unrealized holding gains (losses)	9,421	(1,624)	48,883	(22,632)
Portion of other-than-temporary impairment losses recognized in other comprehensive income (losses)	(2)	7	(4)	(1)
Reclassification adjustment for losses included in net income	(847)	717	(2,665)	1,403
Unrealized foreign currency translation gains (losses)	200	(454)	331	(1,554)
Other comprehensive income (loss), net of tax	8,772	(1,354)	46,545	(22,784)
Comprehensive income (loss), net of tax	$ 15,493	$ 2,374	$ 87,529	$ (6,163)