SEGMENT INFORMATION - Summarized financial information by segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Reconciliation of operating profit loss from segment to consolidated
Premiums earned	$ 167,302	$ 155,786
SAP underwriting profit (loss)	4,970	(7,473)
GAAP adjustments	2,030	364
GAAP underwriting profit (loss)	7,000	(7,109)
Net investment income	12,763	11,371
Net realized investment gains/losses and change in unrealized gains on equity investments	22,643	(5,393)
Other income (loss)	1,535	1,615
Interest expense	171	142
Other expenses	1,485	870
Income (loss) before income tax expense (benefit)	42,285	(528)
Reconciliation of assets from segment to consolidated
Assets	2,350,459		$ 2,242,461
Eliminations	(606,809)		(556,977)
Reclassifications	(1,423)		(6)
Total assets	1,742,227		1,685,478
Property and casualty insurance [Member]
Reconciliation of operating profit loss from segment to consolidated
Premiums earned	124,772	118,632
SAP underwriting profit (loss)	1,407	(9,036)
GAAP adjustments	1,210	262
GAAP underwriting profit (loss)	2,617	(8,774)
Net investment income	9,138	8,148
Net realized investment gains/losses and change in unrealized gains on equity investments	14,168	(3,293)
Other income (loss)	1,533	2,051
Interest expense	171	142
Other expenses	311	233
Income (loss) before income tax expense (benefit)	26,974	(2,243)
Reconciliation of assets from segment to consolidated
Assets	1,220,775		1,191,286
Eliminations	0		0
Reclassifications	(934)		0
Total assets	1,219,841		1,191,286
Reinsurance [Member]
Reconciliation of operating profit loss from segment to consolidated
Premiums earned	42,530	37,154
SAP underwriting profit (loss)	3,563	1,563
GAAP adjustments	820	102
GAAP underwriting profit (loss)	4,383	1,665
Net investment income	3,608	3,218
Net realized investment gains/losses and change in unrealized gains on equity investments	8,542	(2,100)
Other income (loss)	2	(436)
Interest expense	0	0
Other expenses	0	0
Income (loss) before income tax expense (benefit)	16,535	2,347
Reconciliation of assets from segment to consolidated
Assets	512,430		485,270
Eliminations	0		0
Reclassifications	0		0
Total assets	512,430		485,270
Parent company [Member]
Reconciliation of operating profit loss from segment to consolidated
Premiums earned	0	0
SAP underwriting profit (loss)	0	0
GAAP adjustments	0	0
GAAP underwriting profit (loss)	0	0
Net investment income	17	5
Net realized investment gains/losses and change in unrealized gains on equity investments	(67)	0
Other income (loss)	0	0
Interest expense	0	0
Other expenses	1,174	637
Income (loss) before income tax expense (benefit)	(1,224)	$ (632)
Reconciliation of assets from segment to consolidated
Assets	617,254		565,905
Eliminations	(606,809)		(556,977)
Reclassifications	(489)		(6)
Total assets	$ 9,956		$ 8,922