Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 32,104	$ 20,502	$ 62,982	$ 41,612
Change in Net Unrealized Gains (Losses) on Available-For-Sale Investments:
Unrealized Gains (Losses) on Investments arising during the period, net of Deferred Tax	(10,028)	14,684	(44,399)	28,661
Reclassification adjustment for Net Realized Gains (Losses) included in Net Income net of Deferred Tax	(809)	(291)	(2,477)	399
Change in Net Unrealized Gains (Losses) on Investments	(10,837)	14,393	(46,876)	29,060
Change in Other-Than-Temporary Impairments
Non Credit Other-Than-Temporary Impairments arising during the period, net of Deferred Tax	(14)	19	(44)	29
Reclassification Adjustment for Other-Than-Temporary Impairment Credit Losses Recognized in Net Income net of Deferred Tax	0	0	0	389
Change in Other-Than-Temporary Impairments	(14)	19	(44)	418
Change in Foreign Currency Translation Gains (Losses), net of Deferred Tax	(5,880)	785	(3,652)	520
Other Comprehensive Income (Loss)	(16,731)	15,197	(50,572)	29,998
Comprehensive Income	$ 15,373	$ 35,699	$ 12,410	$ 71,610