Investments (Contractual Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Principal Balance by Contractual Maturity, Amount
Due in one year or less	$ 380,099
Due after one year through five years	758,183
Due after five years through ten years	2,686,026
Commercial Mortgage Loans [Member]
Principal Balance by Contractual Maturity, Amount
Due in one year or less	23,869	17,661
Due after one year through five years	44,973	62,851
Due after five years through ten years	44,993	51,720
Due after ten years through fifteen years	8,862	9,423
Due after fifteen years	20,759	21,188
Totals	$ 143,456	$ 162,843
Principal Balance by Contractual Maturity, Percentage
Due in one year or less	16.60%	10.80%
Due after one year through five years	31.30%	38.60%
Due after five years through ten years	31.40%	31.80%
Due after ten years through fifteen years	6.20%	5.80%
Due after fifteen years	14.50%	13.00%
Totals	100.00%	100.00%