Investments - Restricted Cash and Investments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Restricted Cash and Investments Items [Line Items]
Restricted cash and cash equivalents	$ 220,845	$ 77,360
Restricted investments	2,559,667	2,154,338
Restricted cash and investments	2,780,512	2,231,698
Amortized cost	3,382,980	3,132,314
Third party agreements [Member]
Restricted Cash and Investments Items [Line Items]
Restricted cash and cash equivalents	59,272	72,877
Restricted investments	1,059,522	939,800
Amortized cost	1,036,950	933,897
Related party agreements [Member]
Restricted Cash and Investments Items [Line Items]
Restricted cash and cash equivalents	161,047	4,429
Restricted investments	1,491,460	1,201,473
Amortized cost	1,448,698	1,183,156
US state regulatory authorities [Member]
Restricted Cash and Investments Items [Line Items]
Restricted cash and cash equivalents	526	54
Restricted investments	8,685	13,065
Amortized cost	$ 8,474	$ 12,730