Schedule I - Insurance Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net Of Reinsurance (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($) claim	Dec. 31, 2016 USD ($)
Incurred losses and allocated loss adjustment expenses, net of reinsurance
2017	$ 563,255
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance
2017	533,494
All outstanding reserves prior to 2012, net of reinsurance	88
Reserve for unpaid losses and allocated loss adjustment expenses, net of reinsurance	29,849	$ 25,203
2012
Incurred losses and allocated loss adjustment expenses, net of reinsurance
2012	107,873
2013	108,753
2014	114,031
2015	114,067
2016	114,517
2017	114,693
Total of incurred but not reported reserves plus expected development on reported claims	$ 7
Cumulative Number of Reported Claims | claim	16,658
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance
2012	$ 89,603
2013	101,968
2014	107,126
2015	110,782
2016	112,062
2017	113,037
2013
Incurred losses and allocated loss adjustment expenses, net of reinsurance
2013	107,793
2014	108,951
2015	111,006
2016	111,011
2017	111,128
Total of incurred but not reported reserves plus expected development on reported claims	$ 44
Cumulative Number of Reported Claims | claim	15,701
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance
2013	$ 94,238
2014	104,938
2015	108,099
2016	109,662
2017	110,483
2014
Incurred losses and allocated loss adjustment expenses, net of reinsurance
2014	83,784
2015	85,037
2016	84,221
2017	84,289
Total of incurred but not reported reserves plus expected development on reported claims	$ 197
Cumulative Number of Reported Claims | claim	13,146
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance
2014	$ 70,831
2015	79,713
2016	81,684
2017	83,044
2015
Incurred losses and allocated loss adjustment expenses, net of reinsurance
2015	89,646
2016	88,477
2017	88,028
Total of incurred but not reported reserves plus expected development on reported claims	$ 1,231
Cumulative Number of Reported Claims | claim	14,997
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance
2015	$ 71,820
2016	82,940
2017	84,986
2016
Incurred losses and allocated loss adjustment expenses, net of reinsurance
2016	84,771
2017	86,301
Total of incurred but not reported reserves plus expected development on reported claims	$ 3,696
Cumulative Number of Reported Claims | claim	21,363
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance
2016	$ 71,543
2017	80,786
2017
Incurred losses and allocated loss adjustment expenses, net of reinsurance
2017	78,816
Total of incurred but not reported reserves plus expected development on reported claims	$ 5,462
Cumulative Number of Reported Claims | claim	18,624
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance
2017	$ 61,158