Reinsurance - Reinssurance Agreements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Renaissance Reinsurance U.S., Inc.
A.M. Best Rating	A	A
Combined Retention (All 3 Reinsurers)	$ 500,000	$ 500,000
Annual Aggregate Deductible	$ 0	$ 0
Hannover Ruck SE
A.M. Best Rating	A+	A+
Combined Retention (All 3 Reinsurers)	$ 500,000	$ 500,000
Annual Aggregate Deductible	$ 0	$ 0
TOA Reinsurance of America
A.M. Best Rating		A+
Combined Retention (All 3 Reinsurers)		$ 500,000
Annual Aggregate Deductible		$ 0