Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 30,878	$ 21,110
Change in Net Unrealized Gains (Losses) on Available-For-Sale Investments:
Unrealized Gains (Losses) on Investments arising during the period, net of Deferred Tax of $9,623 and $(7,771) in 2018 and 2017, respectively	(34,305)	14,434
Reclassification adjustment for Net Realized Gains (Losses) included in Net Income net of Deferred Tax of $509 and $(114) in 2018 and 2017, respectively	(1,733)	211
Change in Net Unrealized Gains (Losses) on Investments	(36,038)	14,645
Change in Other-Than-Temporary Impairments
Non Credit Other-Than-Temporary Impairments arising during the period, net of Deferred Tax of $9 and $(6) in 2018 and 2017, respectively	(30)	10
Reclassification Adjustment for Other-Than-Temporary Impairment Credit Losses Recognized in Net Income net of Deferred Tax of $0 and $(222) in 2018 and 2017, respectively	0	412
Change in Other-Than-Temporary Impairments	(30)	422
Change in Foreign Currency Translation Gains (Losses), net of Deferred Tax of $(1,082) and $143 in 2018 and 2017, respectively	2,228	(266)
Other Comprehensive Income (Loss)	(33,840)	14,801
Comprehensive Income (Loss)	$ (2,962)	$ 35,911