Investments (Mortgage Loans by Property Type) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Mortgage Loans Property Type Indicators [Line Items]
Recorded investment	$ 2,565,492	$ 2,496,786
Percentage of total	100.00%	100.00%
Apartment
Mortgage Loans Property Type Indicators [Line Items]
Recorded investment	358,152	289,394
Percentage of total	14.00%	11.60%
Retail
Mortgage Loans Property Type Indicators [Line Items]
Recorded investment	740,374	748,731
Percentage of total	28.90%	30.00%
Office building
Mortgage Loans Property Type Indicators [Line Items]
Recorded investment	910,375	917,284
Percentage of total	35.50%	36.70%
Industrial
Mortgage Loans Property Type Indicators [Line Items]
Recorded investment	437,605	439,890
Percentage of total	17.00%	17.60%
Other commercial
Mortgage Loans Property Type Indicators [Line Items]
Recorded investment	$ 118,986	$ 101,487
Percentage of total	4.60%	4.10%