Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Unrealized Gains on Investments arising during the period, Deferred Tax	$ (7,907)	$ (12,788)	$ (15,433)	$ (24,239)
Reclassification adjustment for Net Realized (Gains) Losses included in Net Income, Deferred Tax	157	178	(215)	(760)
Non Credit Other-Than-Temporary Impairments arising during the period, Deferred Tax	(10)	4	(16)	42
Reclassification Adjustment for Other-Than-Temporary Impairment Credit Losses Recognized in Net Income, Deferred Tax	0	(603)	(209)	(709)
Change in Foreign Currency Translation Gains (Losses), Deferred Tax	$ (423)	$ 2,963	$ (280)	$ 3,146