Investments (Impaired Mortgage Loans) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018		Dec. 31, 2018
Financing Receivable Impaired [Line Items]
Unpaid Principal Balance		$ 17,084			$ 30,660
Recorded Investment		17,079			30,635
Related Allowance		0			0
Carrying Value		17,079			30,635
Average Investment	[1]	23,857	$ 14,640
Interest Income		328	56
Impaired mortgage loans with valuation allowance recorded
Financing Receivable Impaired [Line Items]
Unpaid Principal Balance		0			0
Recorded Investment		0			0
Related Allowance		0			0
Carrying Value		0			0
Average Investment		0	0	[1]
Interest Income		0	0
Impaired mortgage loans with no valuation allowance recorded
Financing Receivable Impaired [Line Items]
Unpaid Principal Balance		17,084			30,660
Recorded Investment		17,079			30,635
Related Allowance		0			0
Carrying Value		17,079			$ 30,635
Average Investment		23,857	14,640	[1]
Interest Income		$ 328	$ 56

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