SEGMENT INFORMATION - Summarized financial information by segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Reconciliation of operating profit loss from segment to consolidated
Premiums earned	$ 168,133	$ 157,946	$ 335,435	$ 313,732
SAP underwriting profit (loss)	(13,119)	(16,477)	(8,149)	(23,950)
GAAP adjustments	(1,048)	1,066	982	1,430
GAAP underwriting profit (loss)	(14,167)	(15,411)	(7,167)	(22,520)
Net investment income	12,951	11,778	25,714	23,149
Net realized investment gains/losses and change in unrealized gains on equity investments	4,258	(5,860)	26,901	(11,253)
Other income (loss)	1,557	2,773	3,092	4,388
Interest expense	170	171	341	313
Other expenses	2,788	831	4,273	1,701
Income (loss) before income tax expense (benefit)	1,641	(7,722)	43,926	(8,250)
Reconciliation of assets from segment to consolidated
Assets	2,411,831		2,411,831		$ 2,242,461
Eliminations	(623,505)		(623,505)		(556,977)
Reclassifications	(175)		(175)		(6)
Total assets	1,788,151		1,788,151		1,685,478
Property and casualty insurance [Member]
Reconciliation of operating profit loss from segment to consolidated
Premiums earned	126,297	121,495	251,069	240,127
SAP underwriting profit (loss)	(16,127)	(20,184)	(14,720)	(29,220)
GAAP adjustments	(353)	1,921	857	2,183
GAAP underwriting profit (loss)	(16,480)	(18,263)	(13,863)	(27,037)
Net investment income	9,129	8,410	18,267	16,558
Net realized investment gains/losses and change in unrealized gains on equity investments	2,930	(4,692)	17,098	(7,985)
Other income (loss)	1,551	2,095	3,084	4,146
Interest expense	170	171	341	313
Other expenses	201	244	512	477
Income (loss) before income tax expense (benefit)	(3,241)	(12,865)	23,733	(15,108)
Reconciliation of assets from segment to consolidated
Assets	1,254,989		1,254,989		1,191,286
Eliminations	0		0		0
Reclassifications	0		0		0
Total assets	1,254,989		1,254,989		1,191,286
Reinsurance [Member]
Reconciliation of operating profit loss from segment to consolidated
Premiums earned	41,836	36,451	84,366	73,605
SAP underwriting profit (loss)	3,008	3,707	6,571	5,270
GAAP adjustments	(695)	(855)	125	(753)
GAAP underwriting profit (loss)	2,313	2,852	6,696	4,517
Net investment income	3,808	3,360	7,416	6,578
Net realized investment gains/losses and change in unrealized gains on equity investments	1,545	(1,168)	10,087	(3,268)
Other income (loss)	6	678	8	242
Interest expense	0	0	0	0
Other expenses	0	0	0	0
Income (loss) before income tax expense (benefit)	7,672	5,722	24,207	8,069
Reconciliation of assets from segment to consolidated
Assets	525,750		525,750		485,270
Eliminations	0		0		0
Reclassifications	(101)		(101)		0
Total assets	525,649		525,649		485,270
Parent company [Member]
Reconciliation of operating profit loss from segment to consolidated
Premiums earned	0	0	0	0
SAP underwriting profit (loss)	0	0	0	0
GAAP adjustments	0	0	0	0
GAAP underwriting profit (loss)	0	0	0	0
Net investment income	14	8	31	13
Net realized investment gains/losses and change in unrealized gains on equity investments	(217)	0	(284)	0
Other income (loss)	0	0	0	0
Interest expense	0	0	0	0
Other expenses	2,587	587	3,761	1,224
Income (loss) before income tax expense (benefit)	(2,790)	$ (579)	(4,014)	$ (1,211)
Reconciliation of assets from segment to consolidated
Assets	631,092		631,092		565,905
Eliminations	(623,505)		(623,505)		(556,977)
Reclassifications	(74)		(74)		(6)
Total assets	$ 7,513		$ 7,513		$ 8,922