Investments (AFS Fixed Income securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less fair value	$ 501,398
Due after one year through five years fair value	2,180,671
Due after five years through 10 years fair value	1,589,038
Due after 10 years fair value	79,939
Total AFS fixed income securities	$ 4,351,046	$ 4,066,122