Policy Liabilities and Short Duration Contracts Short Duration Insurance Contracts (Details) $ in Thousands	Dec. 31, 2017 USD ($) claim	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Claims Development [Line Items]
Liabilities for claims and claim adjustment expenses, net of reinsurance	$ 573	$ 543
Property Insurance Product Line [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	9,083
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	8,582
All outstanding liabilities before 2012, net of reinsurance	0
Liabilities for claims and claim adjustment expenses, net of reinsurance	501	500
2013 [Member] | Property Insurance Product Line [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,964	1,964	$ 1,970	$ 1,977	$ 2,058
Total of Incurred-but-Not-Reported Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Reported Claims | claim	328
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,964	1,964	1,964	1,964	$ 1,751
2014 [Member] | Property Insurance Product Line [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,570	1,575	1,650	1,744
Total of Incurred-but-Not-Reported Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Reported Claims | claim	254
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,560	1,560	1,556	$ 1,361
2015 [Member] | Property Insurance Product Line [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,692	1,731	1,777
Total of Incurred-but-Not-Reported Liabilities Plus Expected Development on Reported Claims	$ 4
Cumulative Number of Reported Claims | claim	358
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,638	1,637	$ 1,410
2016 [Member] | Property Insurance Product Line [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,096	2,071
Total of Incurred-but-Not-Reported Liabilities Plus Expected Development on Reported Claims	$ 6
Cumulative Number of Reported Claims | claim	531
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,061	$ 1,680
2017 [Member] | Property Insurance Product Line [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,761
Total of Incurred-but-Not-Reported Liabilities Plus Expected Development on Reported Claims	$ 210
Cumulative Number of Reported Claims | claim	555
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,359