Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 20,502	$ 16,190	$ 41,612	$ 39,122
Change in Net Unrealized Gains on Investments:
Unrealized Gains on Investments arising during the period, net of Deferred Tax	14,684	23,751	28,661	45,018
Reclassification adjustment for Net Realized (Gains) Losses included in Net Income net of Deferred Tax	(291)	(331)	399	1,411
Change in Net Unrealized Gains on Investments	14,393	23,420	29,060	46,429
Change in Other-Than-Temporary Impairments
Non Credit Other-Than-Temporary Impairments arising during the period, net of Deferred Tax	19	(8)	29	(79)
Reclassification Adjustment for Other-Than-Temporary Impairment Credit Losses Recognized in Net Income net of Deferred Tax	0	1,119	389	1,316
Change in Other-Than-Temporary Impairments	19	1,111	418	1,237
Change in Foreign Currency Translation Gains (Losses), net of Deferred Tax	785	(5,493)	520	(5,840)
Other Comprehensive Income	15,197	19,038	29,998	41,826
Comprehensive Income	$ 35,699	$ 35,228	$ 71,610	$ 80,948