Statutory Accounting and Regulation - Equity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, GAAP to Statutory, Increase (Decrease) Due to Investments	$ 1,148
Stockholders' Equity Attributable to Parent	537,125	$ 241,327
Statutory Accounting Practices, GAAP to Statutory, Equity Increase (Decrease) Due to Deferred Policy Acquisition Costs	(35,689)	(15,373)
Statutory Accounting Practices, GAAP to Statutory, Equity Increase (Decrease) Due to Deferred Income Taxes	961	(3,338)
Statutory Accounting Practices, GAAP to Statutory, Equity Increase (Decrease) Due to Investments	955	1,386
Statutory Accounting Practices, GAAP to Statutory, Equity Increase (Decrease) Due to Non-admitted Assets	9	(623)
Statutory Accounting Practices, GAAP to Statutory, Equity Increase (Decrease) Due to Surplus Debentures	10,000	11,176
Statutory Accounting Practices, GAAP to Statutory, Equity Increase (Decrease) Due to Provision for Reinsurance	(3,583)	(7,648)
Statutory Accounting Practices, GAAP to Statutory, Equity Increase (Decrease) Due to Non-statutory Subsidiaries	(138,833)	(32,615)
Statutory Accounting Practices, GAAP to Statutory, Equity Increase (Decrease) Due to Commissions	19,502	18,570
Statutory Accounting Practices, GAAP to Statutory, Equity Increase (Decrease) Due to Prepaid Expenses	(468)	(564)
Statutory Accounting Practices, GAAP to Statutory, Equity Increase (Decrease) Due to Other	(595)	0
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	389,384	212,298
Statutory Accounting Practices, Statutory Net Income Amount	832	6,083	$ 10,520
Family Security Holdings (FSH)
Statutory Accounting Practices [Line Items]
Amount of Restricted Net Assets for Consolidated and Unconsolidated Subsidiaries	26,027
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	22,038	16,269
Statutory Accounting Practices, Statutory Net Income Amount			$ 152
UPC, Subsidiary
Statutory Accounting Practices [Line Items]
Amount of Restricted Net Assets for Consolidated and Unconsolidated Subsidiaries	144,526
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	164,281	155,587
Interboro Insurance Company
Statutory Accounting Practices [Line Items]
Amount of Restricted Net Assets for Consolidated and Unconsolidated Subsidiaries	46,699
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	42,827	40,442
Statutory Accounting Practices, Statutory Net Income Amount		$ 3,513
American Coastal Insurance Company
Statutory Accounting Practices [Line Items]
Amount of Restricted Net Assets for Consolidated and Unconsolidated Subsidiaries	162,234
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	160,238
Statutory Accounting Practices, Statutory Net Income Amount	6,120
Minimum | Family Security Holdings (FSH)
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus Required	3,250
Minimum | UPC, Subsidiary
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus Required	45,187
Minimum | Interboro Insurance Company
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus Required	4,700
Minimum | American Coastal Insurance Company
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus Required	$ 16,565