Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Unrealized gains (losses) on investments arising during the period, deferred tax	$ 1,300	$ (549)	$ (23,349)	$ 9,858
Reclassification adjustment for net realized (gains) losses included in net income, deferred tax	279	293	(780)	1,472
Non credit other-than-temporary impairments arising during the period, deferred tax	(8)	8	34	17
Reclassification adjustment for other-than-temporary impairment credit losses recognized in net income, deferred tax	0	(101)	0	(170)
Change in foreign currency translation gains (losses), deferred tax	$ 175	$ (1)	$ 3,322	$ (6)