LOSS AND LOSS ADJUSTMENT RESERVES - (Schedule of Cumulative Paid Losses and ALAE, Net of Reinsurance Recoverable) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Claims Development [Line Items]
Unfavorable loss and LAE reserve	$ 540,367	$ 324,362	$ 296,230	$ 230,515
Homeowners
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	1,256,685
Unfavorable loss and LAE reserve	149,314
Homeowners | 2011
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	26,342	26,340	26,287	25,982	$ 25,580	$ 24,047	$ 22,723	$ 21,323	$ 19,250	$ 11,119
Homeowners | 2012
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	26,901	26,861	26,777	26,113	25,186	23,923	23,120	20,728	13,693
Homeowners | 2013
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	37,915	37,688	37,473	35,803	35,123	33,867	31,606	19,986
Homeowners | 2014
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	61,692	61,441	60,555	59,722	57,891	53,831	37,033
Homeowners | 2015
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	93,405	92,327	90,415	86,647	79,359	52,214
Homeowners | 2016
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	153,997	152,258	148,274	142,716	102,556
Homeowners | 2017
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	178,013	179,327	176,580	135,589
Homeowners | 2018
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	206,133	194,160	141,173
Homeowners | 2019
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	236,090	157,768
Homeowners | 2020
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	236,197
Homeowners | All outstanding liabilities for unpaid claims and ALAE prior to 2011, net of reinsurance
Claims Development [Line Items]
Unfavorable loss and LAE reserve	0
Commercial general liability
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	47,437
Unfavorable loss and LAE reserve	28,328
Commercial general liability | 2011
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	7,693	7,365	6,349	5,831	4,866	4,246	3,673	3,366	2,763	764
Commercial general liability | 2012
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	4,790	4,521	4,098	3,841	3,686	3,342	2,632	1,714	871
Commercial general liability | 2013
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	5,847	5,467	5,033	4,606	3,867	3,366	2,233	882
Commercial general liability | 2014
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	6,901	6,270	5,130	4,375	3,855	2,593	717
Commercial general liability | 2015
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	6,566	5,866	3,827	3,249	2,296	798
Commercial general liability | 2016
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	8,382	6,606	5,088	3,657	1,515
Commercial general liability | 2017
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	4,225	3,293	2,478	1,592
Commercial general liability | 2018
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	2,604	1,554	963
Commercial general liability | 2019
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	424	147
Commercial general liability | 2020
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	5
Commercial general liability | All outstanding liabilities for unpaid claims and ALAE prior to 2011, net of reinsurance
Claims Development [Line Items]
Unfavorable loss and LAE reserve	3,545
Automobile
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	67,350
Unfavorable loss and LAE reserve	1,388
Automobile | 2011
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	2,755	2,755	2,755	2,755	2,755	2,726	2,644	2,562	2,381	$ 1,417
Automobile | 2012
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	1,449	1,447	1,444	1,430	1,393	1,384	1,333	1,293	$ 867
Automobile | 2013
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	2,116	2,116	2,112	2,109	2,069	1,906	1,609	$ 907
Automobile | 2014
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	4,396	4,383	4,291	4,122	3,678	3,120	$ 1,455
Automobile | 2015
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	2,897	2,890	2,807	2,670	2,293	$ 1,393
Automobile | 2016
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	26,132	25,582	23,053	17,258	$ 8,084
Automobile | 2017
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	24,468	23,860	20,762	$ 12,821
Automobile | 2018
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	3,137	3,626	$ 2,331
Automobile | 2019
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	0	$ (5)
Automobile | 2020
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	0
Automobile | All outstanding liabilities for unpaid claims and ALAE prior to 2011, net of reinsurance
Claims Development [Line Items]
Unfavorable loss and LAE reserve	$ 15