Investments (Contractual Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Principal Balance by Contractual Maturity, Amount
Due in one year or less	$ 213,353
Due after one year through five years	1,181,707
Due after five years through ten years	3,448,906
Totals	6,841,543	6,510,320
Commercial Mortgage Loans [Member]
Principal Balance by Contractual Maturity, Amount
Due in one year or less	16,390	10,491
Due after one year through five years	83,965	51,304
Due after five years through ten years	30,591	51,839
Due after ten years through fifteen years	0	0
Due after fifteen years	19,813	20,300
Totals	$ 150,759	$ 133,934
Principal Balance by Contractual Maturity, Percentage
Due in one year or less	10.90%	7.80%
Due after one year through five years	55.70%	38.30%
Due after five years through ten years	20.30%	38.70%
Due after ten years through fifteen years	0.00%	0.00%
Due after fifteen years	13.10%	15.20%
Totals	100.00%	100.00%