SEGMENT INFORMATION - Summarized financial information by segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Reconciliation of operating profit loss from segment to consolidated
Premiums earned	$ 157,946	$ 149,837	$ 313,732	$ 294,324
SAP underwriting profit (loss)	(16,477)	(8,674)	(23,950)	(8,021)
GAAP adjustments	1,066	1,201	1,430	(1,417)
GAAP underwriting profit (loss)	(15,411)	(7,473)	(22,520)	(9,438)
Net investment income	11,778	11,171	23,149	22,178
Net realized investment gains (losses) and, beginning in 2018, change in unrealized investment gains on equity investments	(5,860)	3,387	(11,253)	2,760
Other income (loss)	2,773	1,031	4,388	1,901
Interest expense	171	85	313	169
Other expenses	831	802	1,701	1,563
Income (loss) before income tax expense (benefit)	(7,722)	7,229	(8,250)	15,669
Reconciliation of assets from segment to consolidated
Assets	2,222,096		2,222,096		$ 2,289,419
Eliminations	(562,043)		(562,043)		(599,036)
Reclassifications	(745)		(745)		(8,443)
Total assets	1,659,308		1,659,308		1,681,940
Property and casualty insurance [Member]
Reconciliation of operating profit loss from segment to consolidated
Premiums earned	121,495	116,187	240,127	229,835
SAP underwriting profit (loss)	(20,184)	(8,892)	(29,220)	(11,486)
GAAP adjustments	1,921	2,006	2,183	(281)
GAAP underwriting profit (loss)	(18,263)	(6,886)	(27,037)	(11,767)
Net investment income	8,410	7,958	16,558	15,973
Net realized investment gains (losses) and, beginning in 2018, change in unrealized investment gains on equity investments	(4,692)	3,738	(7,985)	3,141
Other income (loss)	2,095	1,559	4,146	3,000
Interest expense	171	85	313	169
Other expenses	244	231	477	410
Income (loss) before income tax expense (benefit)	(12,865)	6,053	(15,108)	9,768
Reconciliation of assets from segment to consolidated
Assets	1,176,071		1,176,071		1,200,636
Eliminations	0		0		0
Reclassifications	0		0		(1,393)
Total assets	1,176,071		1,176,071		1,199,243
Reinsurance [Member]
Reconciliation of operating profit loss from segment to consolidated
Premiums earned	36,451	33,650	73,605	64,489
SAP underwriting profit (loss)	3,707	218	5,270	3,465
GAAP adjustments	(855)	(805)	(753)	(1,136)
GAAP underwriting profit (loss)	2,852	(587)	4,517	2,329
Net investment income	3,360	3,201	6,578	6,184
Net realized investment gains (losses) and, beginning in 2018, change in unrealized investment gains on equity investments	(1,168)	(351)	(3,268)	(381)
Other income (loss)	678	(528)	242	(1,099)
Interest expense	0	0	0	0
Other expenses	0	0	0	0
Income (loss) before income tax expense (benefit)	5,722	1,735	8,069	7,033
Reconciliation of assets from segment to consolidated
Assets	477,701		477,701		484,678
Eliminations	0		0		0
Reclassifications	(745)		(745)		(6,273)
Total assets	476,956		476,956		478,405
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	8	12	13	21
Net realized investment gains (losses) and, beginning in 2018, change in unrealized investment gains on equity investments	0	0	0	0
Other income (loss)	0	0	0	0
Interest expense	0	0	0	0
Other expenses	587	571	1,224	1,153
Income (loss) before income tax expense (benefit)	(579)	$ (559)	(1,211)	$ (1,132)
Reconciliation of assets from segment to consolidated
Assets	568,324		568,324		604,105
Eliminations	(562,043)		(562,043)		(599,036)
Reclassifications	0		0		(777)
Total assets	$ 6,281		$ 6,281		$ 4,292