Liability for Unpaid Claims - Short-Duration Contracts (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Claims Development [Line Items]
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 23,193	$ 26,721
2013 [Member]
Claims Development [Line Items]
Total of incurred-but-not-reported liabilities plus expected development on reported claims	0
2014 [Member]
Claims Development [Line Items]
Total of incurred-but-not-reported liabilities plus expected development on reported claims	1
2015 [Member]
Claims Development [Line Items]
Total of incurred-but-not-reported liabilities plus expected development on reported claims	46
2016 [Member]
Claims Development [Line Items]
Total of incurred-but-not-reported liabilities plus expected development on reported claims	1,022
2017 [Member]
Claims Development [Line Items]
Total of incurred-but-not-reported liabilities plus expected development on reported claims	$ 22,124