Investments (Mortgage Loans by Real Estate Geographic Location) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Mortgage Loans On Real Estate Geographic Location Of Property [Line Items]
Recorded investment	$ 2,496,251	$ 2,312,167
Percentage of total	100.00%	100.00%
Pacific
Mortgage Loans On Real Estate Geographic Location Of Property [Line Items]
Recorded investment	658,054	593,589
Percentage of total	26.40%	25.70%
South Atlantic
Mortgage Loans On Real Estate Geographic Location Of Property [Line Items]
Recorded investment	581,781	477,068
Percentage of total	23.30%	20.50%
Mountain
Mortgage Loans On Real Estate Geographic Location Of Property [Line Items]
Recorded investment	260,794	233,174
Percentage of total	10.40%	10.10%
Middle Atlantic
Mortgage Loans On Real Estate Geographic Location Of Property [Line Items]
Recorded investment	269,602	300,475
Percentage of total	10.80%	13.00%
West North Central
Mortgage Loans On Real Estate Geographic Location Of Property [Line Items]
Recorded investment	181,937	168,063
Percentage of total	7.30%	7.30%
East North Central
Mortgage Loans On Real Estate Geographic Location Of Property [Line Items]
Recorded investment	239,997	224,122
Percentage of total	9.60%	9.70%
West South Central
Mortgage Loans On Real Estate Geographic Location Of Property [Line Items]
Recorded investment	155,061	161,451
Percentage of total	6.20%	7.00%
East South Central
Mortgage Loans On Real Estate Geographic Location Of Property [Line Items]
Recorded investment	67,155	62,789
Percentage of total	2.70%	2.70%
New England
Mortgage Loans On Real Estate Geographic Location Of Property [Line Items]
Recorded investment	$ 81,870	$ 91,436
Percentage of total	3.30%	4.00%