VARIABLE INTEREST ENTITY - (Carrying Amount of VIE Consolidated Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments
Debt securities, available-for-sale, at amortized cost	$ 422,300	$ 376,644
Equity securities, available-for-sale, at fair value	15,434	29,375
Total investments (including $26,284 and $28,704 related to the VIE, respectively)	444,021	409,682
Cash and cash equivalents	86,228	74,593	$ 53,038	$ 40,157
Reinsurance recoverable	124,601	47,863
Prepaid reinsurance premiums	135,492	156,932
Premiums receivable, net	46,393	54,854
Deferred acquisition costs	40,893	41,892
Other assets	13,403	11,509
TOTAL ASSETS	904,873	815,390
Liabilities:
Loss and loss adjustment expense reserves	230,515	158,110	$ 97,706	$ 78,330
Unearned premiums	294,423	294,022
Reinsurance payable	71,944	79,154
Debt	49,251	4,909
Other liabilities	25,059	37,643
Total liabilities	677,414	580,925
Monarch Delaware - Variable Interest Entity [Member]
Investments
Debt securities, available-for-sale, at amortized cost	25,111	27,100
Equity securities, available-for-sale, at fair value	1,173	1,604
Total investments (including $26,284 and $28,704 related to the VIE, respectively)	26,284	28,704
Cash and cash equivalents	14,211	15,668
Reinsurance recoverable	3,323	0
Prepaid reinsurance premiums	2,481	1,070
Premiums receivable, net	1,184	1,584
Deferred acquisition costs	1,722	1,539
Other assets	2,322	371
TOTAL ASSETS	51,527	48,936
Liabilities:
Loss and loss adjustment expense reserves	6,356	1,659
Unearned premiums	8,752	8,406
Reinsurance payable	1,802	864
Debt	4,930	4,909
Other liabilities	1,825	1,026
Total liabilities	$ 23,665	$ 16,864