Reinsurance - Narrative (Details) - USD ($)		3 Months Ended			9 Months Ended
	Jun. 30, 2019	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Effects of Reinsurance [Line Items]
Ceded premiums		$ 28,440,000		$ 25,327,000	$ 100,260,000	$ 79,970,000
Quota Share Reinsurance Agreement, 2019
Effects of Reinsurance [Line Items]
Contingent termination fee					$ 0
Threshold for private mortgage insurer eligibility requirements for termination election (less than) (as a percent)					90.00%
Quota share for all policies covered (as a percent)					30.00%
Cede rate, option 1 (as a percent)					25.00%
Cede rate, option 2 (as a percent)					20.00%
Ceding commission, percentage (as a percent)					20.00%
Loss ratio threshold for profit commissions (as a percent)					62.00%
Quota Share Reinsurance Agreement, 2015
Effects of Reinsurance [Line Items]
Contingent termination fee		$ 0	$ 6,800,000
Threshold for private mortgage insurer eligibility requirements for termination election (less than) (as a percent)		90.00%
Quota share for all policies covered (as a percent)	30.00%	15.00%
Loss ratio threshold for profit commissions (as a percent)		68.00%
Excess of Loss Reinsurance Agreement, Home Re
Effects of Reinsurance [Line Items]
Ceded premiums		$ 5,400,000			$ 12,400,000