Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Unrealized gains (losses) on investments arising during the period, deferred tax	$ 3,730	$ 2,624	$ (14,925)
Reclassification adjustment for net realized (gains) losses included in net income, deferred tax	(846)	9,185	2,776
Non credit other-than-temporary impairments arising during the period, deferred tax	27	60	(48)
Reclassification adjustment for other-than-temporary impairment credit losses recognized in net income, deferred tax	0	(90)	0
Change in foreign currency translation gains (losses), deferred tax	$ 5,017	$ 351	$ 2,800