Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Unrealized Gains (Losses) on Investments arising during the period, Deferred Tax	$ 1,821	$ (5,197)	$ 13,543	$ (19,884)
Reclassification adjustment for Net Realized (Gains) Losses included in Net Income, Deferred Tax	(84)	881	992	(72)
Non Credit Other-Than-Temporary Impairments arising during the period, Deferred Tax	3	(6)	20	(21)
Reclassification Adjustment for Other-Than-Temporary Impairment Credit Losses Recognized in Net Income, Deferred Tax	0	(193)	0	(410)
Change in Foreign Currency Translation Gains (Losses), Deferred Tax	$ 73	$ (691)	$ 2,516	$ (971)