Securities in an Unrealized Loss Position (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Securities in continuous unrealized loss position fair value	$ 4,981,337,000	$ 5,160,888,000
Securities in continuous unrealized loss position, aggregate losses accumulated In AOCI	64,786,000	99,268,000
Fixed Maturity Securities
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment	0	0
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment	$ 0	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Other	1
Securities in continuous unrealized loss position fair value	$ 23,077,000	22,034,000
Securities in continuous unrealized loss position, aggregate losses accumulated In AOCI	2,597,000	3,639,000
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment	$ 0	18,100,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Other	3
Securities in continuous unrealized loss position fair value	$ 18,631,000	9,091,000
Securities in continuous unrealized loss position, aggregate losses accumulated In AOCI	$ 1,960,000	$ 1,046,000