Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Unrealized gains on investments arising during the period, deferred tax	$ (7,771)	$ (11,737)
Reclassification adjustment for net realized losses included in net income, deferred tax	(114)	(758)
Non credit other-than-temporary impairments arising during the period, deferred tax	(6)	38
Reclassification adjustment for other-than-temporary impairment credit losses recognized in net income, deferred tax	(222)	0
Change in foreign currency translation losses, deferred tax	$ 143	$ 183