Investments (Mortgage Loans by Property Type) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Mortgage Loans Property Type Indicators [Line Items]
Recorded investment	$ 2,534,694	$ 2,496,786
Percentage of total	100.00%	100.00%
Apartment
Mortgage Loans Property Type Indicators [Line Items]
Recorded investment	346,918	289,394
Percentage of total	13.70%	11.60%
Retail
Mortgage Loans Property Type Indicators [Line Items]
Recorded investment	720,921	748,731
Percentage of total	28.40%	30.00%
Office building
Mortgage Loans Property Type Indicators [Line Items]
Recorded investment	917,985	917,284
Percentage of total	36.20%	36.70%
Industrial
Mortgage Loans Property Type Indicators [Line Items]
Recorded investment	412,322	439,890
Percentage of total	16.30%	17.60%
Other commercial
Mortgage Loans Property Type Indicators [Line Items]
Recorded investment	$ 136,548	$ 101,487
Percentage of total	5.40%	4.10%