Investments (Net Realized Gains (Losses) on Invesments) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gain (Loss) on Investments [Line Items]
Net realized gains (losses) on investments, excluding other than temporary impairment (OTTI) losses	$ 2,719	$ 1,579	$ 3,873	$ 2,338	$ 844	$ 5,256	$ 2,737	$ 2,687	$ 10,509	$ 11,524	$ 10,211
Fixed Maturity Securities [Member]
Gain (Loss) on Investments [Line Items]
Gross realized gains									18,254	14,132	7,230
Gross realized losses									(9,058)	(4,036)	(5,787)
Gross realized gains (losses), excluding other than temporary impairments									9,196	10,096	1,443
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Gross realized gains									348	0	0
Other Investments [Member]
Gain (Loss) on Investments [Line Items]
Gain on sale of real estate									56	884	4,194
Loss on sale of real estate									0	(93)	(575)
Impairment losses on real estate									0	0	(1,297)
Gain (loss) on other investments									56	791	2,322
Mortgage Loans on Real Estate [Member]
Gain (Loss) on Investments [Line Items]
Decrease (increase) in allowance for credit losses									278	(4,846)	1,018
Recovery of specific allowance									631	5,483	5,428
Change in allowance for credit losses and recoveries									$ 909	$ 637	$ 6,446