LOSS AND LOSS ADJUSTMENT RESERVES - (Schedule of Cumulative Paid Losses and ALAE, Net of Reinsurance Recoverable) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Claims Development [Line Items]
Unfavorable loss and LAE reserve	$ 230,515	$ 158,110	$ 97,706	$ 78,330
Homeowners [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	585,584
Unfavorable loss and LAE reserve	99,650
Homeowners [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	15,587	15,587	15,583	15,595	$ 15,445	$ 15,308	$ 15,190	$ 14,689	$ 13,832	$ 9,477
Homeowners [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	27,049	26,982	26,927	26,831	26,462	26,007	24,657	23,095	15,047
Homeowners [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	30,376	29,739	29,092	27,984	26,886	24,730	21,350	14,052
Homeowners [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	25,982	25,580	24,047	22,723	21,323	19,250	11,119
Homeowners [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	26,113	25,186	23,923	23,120	20,728	13,693
Homeowners [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	35,803	35,123	33,867	31,606	19,986
Homeowners [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	59,722	57,891	53,831	37,033
Homeowners [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	86,647	79,359	52,214
Homeowners [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	142,716	102,556
Homeowners [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	135,589
Homeowners [Member] | All outstanding liabilities for unpaid claims and LAE prior to 2008, net of reinsurance
Claims Development [Line Items]
Unfavorable loss and LAE reserve	88
Commercial General Liability [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	65,783
Unfavorable loss and LAE reserve	17,111
Commercial General Liability [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	19,693	17,716	16,122	15,389	14,662	12,768	10,980	8,856	6,491	2,324
Commercial General Liability [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	11,308	10,454	10,130	8,593	8,046	7,384	6,466	4,236	2,253
Commercial General Liability [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	7,631	7,382	7,238	6,363	5,553	3,855	2,279	1,187
Commercial General Liability [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	5,831	4,866	4,246	3,673	3,366	2,763	764
Commercial General Liability [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	3,841	3,686	3,342	2,632	1,714	871
Commercial General Liability [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	4,606	3,867	3,366	2,233	882
Commercial General Liability [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	4,375	3,855	2,593	717
Commercial General Liability [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	3,249	2,296	798
Commercial General Liability [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	3,657	1,515
Commercial General Liability [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	1,592
Commercial General Liability [Member] | All outstanding liabilities for unpaid claims and LAE prior to 2008, net of reinsurance
Claims Development [Line Items]
Unfavorable loss and LAE reserve	383
Personal Auto Liability [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	46,997
Unfavorable loss and LAE reserve	11,030
Personal Auto Liability [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	554	554	554	554	554	554	541	519	513	$ 442
Personal Auto Liability [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	243	243	243	243	241	225	220	218	$ 61
Personal Auto Liability [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	3,035	2,984	2,978	2,942	2,863	2,715	2,482	$ 1,713
Personal Auto Liability [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	2,755	2,755	2,726	2,644	2,562	2,381	$ 1,417
Personal Auto Liability [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	1,430	1,393	1,384	1,333	1,293	$ 867
Personal Auto Liability [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	2,109	2,069	1,906	1,609	$ 907
Personal Auto Liability [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	4,122	3,678	3,120	$ 1,455
Personal Auto Liability [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	2,670	2,293	$ 1,393
Personal Auto Liability [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	17,258	$ 8,084
Personal Auto Liability [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	12,821
Personal Auto Liability [Member] | All outstanding liabilities for unpaid claims and LAE prior to 2008, net of reinsurance
Claims Development [Line Items]
Unfavorable loss and LAE reserve	$ 29