Investments (Credit Losses Recorded in Earnings) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings:
Balance beginning of period	$ 1,313	$ 1,158
Additional credit losses recognized during the period, related to securities for which:
No OTTI has been previously recognized	0	171
Accumulated credit losses related to impaired debt securities, Ending Balance	$ 1,313	$ 1,329