Investments (Pledged Assets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
In favor of ceding companies, other counterparties, or government authorities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Restricted cash, cash equivalents and investments	$ 3,585,792	$ 2,894,401
Pledged as collateral for letter of credity facility
Schedule of Trading Securities and Other Trading Assets [Line Items]
Restricted cash, cash equivalents and investments	$ 571,750	$ 1,053,632

Cash and investments whose use in whole or in part is restricted for the long-term, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

No definition available.

Name:	us-gaap_RestrictedCashAndInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant