Investments (Impaired Mortgage Loans) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Financing Receivable Impaired [Line Items]
Unpaid Principal Balance		$ 6,427		$ 6,427		$ 2,758
Recorded Investment		5,856		5,856		2,216
Related Allowance		0		0		0
Carrying Value		5,856		5,856		2,216
Average Investment	[1]	3,967	$ 6,953	3,062	$ 10,146
Interest Income		33	107	100	324
Impaired mortgage loans with valuation allowance recorded
Financing Receivable Impaired [Line Items]
Unpaid Principal Balance		0		0		0
Recorded Investment		0		0		0
Related Allowance		0		0		0
Carrying Value		0		0		0
Average Investment	[1]	0	0	0	5,459
Interest Income		0	0	0	0
Impaired mortgage loans with no valuation allowance recorded
Financing Receivable Impaired [Line Items]
Unpaid Principal Balance		6,427		6,427		2,758
Recorded Investment		5,856		5,856		2,216
Related Allowance		0		0		0
Carrying Value		5,856		5,856		$ 2,216
Average Investment	[1]	3,967	6,953	3,062	4,687
Interest Income		$ 33	$ 107	$ 100	$ 324

[1] Average recorded investment represents the average loan balances as of the beginning of period and all subsequent quarterly end of period balances.