Investments (Impaired Mortgage Loans) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Financing Receivable Impaired [Line Items]
Unpaid Principal Balance		$ 2,620		$ 2,620		$ 2,758
Recorded Investment		2,077		2,077		2,216
Related Allowance		0		0		0
Carrying Value		2,077		2,077		2,216
Average Investment	[1]	2,088	$ 8,625	2,131	$ 11,224
Interest Income		33	107	67	216
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	4,724	0	7,279
Interest Income		0	0	0	0
Impaired mortgage loans with no valuation allowance recorded
Financing Receivable Impaired [Line Items]
Unpaid Principal Balance		2,620		2,620		2,758
Recorded Investment		2,077		2,077		2,216
Related Allowance		0		0		0
Carrying Value		2,077		2,077		$ 2,216
Average Investment	[1]	2,088	3,901	2,131	3,945
Interest Income		$ 33	$ 107	$ 67	$ 216

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