Consolidated Statements of Comprehensive Income (Loss) - 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]
Net Income (Loss)	$ 4,625	$ (27,979)	$ 67,607	$ 13,633
Change in Net Unrealized Gains (Losses) on Available-For-Sale Investments:
Unrealized Gains (Losses) on Investments arising during the period, net of Deferred Tax	(6,844)	9,653	(50,706)	36,928
Reclassification adjustment for Net Realized Gains (Losses) included in Net Income net of Deferred Tax	318	(1,636)	(2,699)	134
Change in Net Unrealized Gains (Losses) on Investments	(6,526)	8,017	(53,405)	37,062
Change in Other-Than-Temporary Impairments
Non Credit Other-Than-Temporary Impairments arising during the period, net of Deferred Tax	(12)	9	(56)	39
Reclassification Adjustment for Other-Than-Temporary Impairment Credit Losses Recognized in Net Income net of Deferred Tax	0	358	0	761
Change in Other-Than-Temporary Impairments	(12)	367	(56)	800
Change in Foreign Currency Translation Gains (Losses), net of Deferred Tax	(768)	1,284	(4,420)	1,803
Other Comprehensive Income (Loss)	(7,306)	9,668	(57,881)	39,665
Comprehensive Income (Loss)	$ (2,681)	$ (18,311)	$ 9,726	$ 53,298