Investments (Impaired Mortgage Loans) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Financing Receivable Impaired [Line Items]
Unpaid Principal Balance		$ 17,017		$ 17,017		$ 30,660
Recorded Investment		17,014		17,014		30,635
Related Allowance		0		0		0
Carrying Value		17,014		17,014		30,635
Average Investment	[1]	17,047	$ 27,038	21,576	$ 19,978
Interest Income		171	247	499	304
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	0
Interest Income		0	0	0	0
Impaired mortgage loans with no valuation allowance recorded
Financing Receivable Impaired [Line Items]
Unpaid Principal Balance		17,017		17,017		30,660
Recorded Investment		17,014		17,014		30,635
Related Allowance		0		0		0
Carrying Value		17,014		17,014		$ 30,635
Average Investment	[1]	17,047	27,038	21,576	19,978
Interest Income		$ 171	$ 247	$ 499	$ 304

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