Mortgage Loans on Real Estate (Aging of Financing Receivables) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Commercial mortgage loans, past due	$ 0	$ 0
Commercial mortgage loans, current	2,449,909	2,451,760
Commercial mortgage loans, collateral dependent receivables	0	5,961
Principal outstanding	2,449,909	2,457,721	$ 2,607,698
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Commercial mortgage loans, past due	0	0
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Commercial mortgage loans, past due	0	0
90 Days and Over Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Commercial mortgage loans, past due	$ 0	$ 0