Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 40,494	$ 82,726	$ 81,057
Change in Net Unrealized Gains (Losses) on Investments:
Unrealized Gains (Losses) on Investments arising during the period, net of Deferred Tax of $(8,748), $3,730 and $2,624 in 2017, 2016 and 2015, respectively	23,123	(6,927)	(5,331)
Reclassification adjustment for Net Realized Gains included in Net Income net of Deferred Tax of $5,335, $(846) and $9,185 in 2017, 2016 and 2015, respectively	(14,100)	1,572	(17,058)
Change in Net Unrealized Gains (Losses) on Investments	9,023	(5,355)	(22,389)
Change in Other-Than-Temporary Impairments
Non Credit Other-Than-Temporary Impairments arising during the period, net of Deferred Tax of $(16), $27 and $60 in 2017, 2016 and 2015, respectively	40	(50)	(112)
Reclassification Adjustment for Other-Than-Temporary Impairment Credit Losses Recognized in Net Income net of Deferred Tax of $0, $0 and $(90) in 2017, 2016 and 2015, respectively	0	0	168
Change in Other-Than-Temporary Impairments	40	(50)	56
Change in Foreign Currency Translation Gains (Losses), net of Deferred Tax of $(2,874), $5,017 and $351 in 2017, 2016 and 2015, respectively	1,930	(9,324)	(622)
Other Comprehensive Income (Loss)	10,993	(14,729)	(22,955)
Comprehensive Income	$ 51,487	$ 67,997	$ 58,102