Related Party Transactions - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Legal Fees
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	$ 3,188	$ 2,892
Spouse of Executive Officer | Legal Fees
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	$ 1,594	$ 1,446
Related interest in billings (percentage)	50.00%
Director
Related Party Transaction [Line Items]
Related interest in billings (percentage)	7.70%
Director | AmRisc gross written premiums
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	$ 220,150
Director | AmRisc Fees and Commission
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	60,016
Director | AmRisc ceded premiums written
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	3,564
Director | AmRisc Rent
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	25
Director | AmRisc net premiums receivable
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	$ 29,913