Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Unrealized Gains (Losses) on Investments arising during the period, Deferred Tax	$ 9,623	$ (7,771)
Reclassification adjustment for Net Realized (Gains) Losses included in Net Income, Deferred Tax	509	(114)
Non Credit Other-Than-Temporary Impairments arising during the period, Deferred Tax	9	(6)
Reclassification Adjustment for Other-Than-Temporary Impairment Credit Losses Recognized in Net Income, Deferred Tax	0	(222)
Change in Foreign Currency Translation Gains (Losses), Deferred Tax	$ (1,082)	$ 143