Reserves for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves for unpaid losses and loss adjustment expenses, beginning of year	$ 267,493	$ 194,602
Commutations of MLQS	0	27,929
Adjusted net reserves for losses and loss adjustment expenses, beginning of year	267,493	222,531
Incurred losses and loss adjustment expenses:
Current year	30,183	27,211
Prior years	(1,284)	(5,104)
Total net losses and loss adjustment expenses incurred	28,899	22,107
Payments:
Current year	340	333
Prior years	17,516	11,566
Total payments	17,856	11,899
Net reserves for unpaid losses and loss adjustment expenses, end of period	278,536	232,739
Reinsurance recoverable on unpaid losses	49,673	40,262
Gross reserves for unpaid losses and loss adjustment expenses, end of period	$ 328,209	$ 273,001