Mortgage Loans on Real Estate (Schedule of Financing Receivables Past Due) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Commercial mortgage loans, past due	$ 0	$ 0
Commercial mortgage loans, current	2,427,905	2,449,909
Commercial mortgage loans, collateral dependent receivables	0	0
Principal outstanding	2,427,905	2,449,909
30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Commercial mortgage loans, past due	0	0
60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Commercial mortgage loans, past due	0	0
90 Days and Over [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Commercial mortgage loans, past due	$ 0	$ 0