Investments (Mortgage Loans by Property Type) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Mortgage Loans on Real Estate [Line Items]
Recorded investment	$ 2,623,933	$ 2,496,786
Percentage of total	100.00%	100.00%
Apartment
Mortgage Loans on Real Estate [Line Items]
Recorded investment	371,209	289,394
Percentage of total	14.10%	11.60%
Retail
Mortgage Loans on Real Estate [Line Items]
Recorded investment	792,978	748,731
Percentage of total	30.20%	30.00%
Office building
Mortgage Loans on Real Estate [Line Items]
Recorded investment	859,402	917,284
Percentage of total	32.80%	36.70%
Industrial
Mortgage Loans on Real Estate [Line Items]
Recorded investment	457,945	439,890
Percentage of total	17.50%	17.60%
Other commercial
Mortgage Loans on Real Estate [Line Items]
Recorded investment	$ 142,399	$ 101,487
Percentage of total	5.40%	4.10%