Investments - Gross Mortgage Loan Principal Outstanding and Allowance for Potential Future Losses (Details) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2014
Dec. 31, 2013
Investments [Abstract]    
Principal outstanding $ 572,811 $ 632,507
Allowance for potential future losses (2,325) (3,251)
Mortgage loans, carrying value $ 570,486 $ 629,256