Investments (Details 7) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Gross mortgage loan principal outstanding and allowance for potential future losses    
Principal outstanding $ 582,017 $ 604,772
Allowance for potential future losses (2,517) (2,849)
Carrying value $ 579,500 $ 601,923