OPERATING SEGMENT INFORMATION - Summary of Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
REVENUES
Net premiums earned	$ 204,002	$ 200,815	$ 196,522	$ 190,027	$ 188,296	$ 182,025	$ 184,331	$ 183,285	$ 791,366	$ 737,937	$ 728,608
Net investment income	16,962	16,314	14,577	14,232	14,446	14,187	13,238	13,005	62,085	54,876	53,075
Net realized gains	15,507	18,647	20,849	8,404	5,111	35	(1,359)	624	63,407	4,411	34,645
Net unrealized losses on equity securities	(64,200)	4,848	(12,611)	(26,772)					(98,735)
Consolidated revenue									818,123	797,224	816,328
INSURANCE EXPENSES
Loss and settlement expenses									428,193	401,584	349,778
Policy acquisition costs									267,738	252,515	249,612
Other insurance expenses									53,803	56,994	53,093
Insurance expenses									749,734	711,093	652,483
NET EARNINGS
Net underwriting income									41,632	26,844	76,125
Net investment income	16,962	16,314	14,577	14,232	14,446	14,187	13,238	13,005	62,085	54,876	53,075
Net realized gains	15,507	18,647	20,849	8,404	5,111	35	(1,359)	624	63,407	4,411	34,645
Net unrealized losses on equity securities	(64,200)	4,848	(12,611)	(26,772)					(98,735)
General corporate expense and interest on debt									(16,864)	(18,766)	(17,596)
Equity in earnings of unconsolidated investees									16,056	17,224	10,833
Earnings before income taxes	(32,708)	46,349	39,562	14,378	24,972	(862)	34,036	26,443	67,581	84,589	157,082
Income tax expense									3,402	(20,439)	42,162
Net earnings	$ (20,660)	$ 39,372	$ 33,251	$ 12,216	$ 57,258	$ 1,734	$ 26,208	$ 19,828	$ 64,179	105,028	114,920
Maui Jim Inc.
Segment reporting information
Ownership percentage	40.00%								40.00%
Prime Holdings Insurance Services, Inc. (Prime)
Segment reporting information
Ownership percentage	23.00%								23.00%
Casualty segment
REVENUES
Net premiums earned									$ 523,472	478,603	454,843
INSURANCE EXPENSES
Loss and settlement expenses									329,763	305,679	259,907
Policy acquisition costs									151,007	136,135	128,566
Other insurance expenses									31,562	32,885	30,040
NET EARNINGS
Net underwriting income									11,140	3,904	36,329
Property segment
REVENUES
Net premiums earned									149,261	138,346	152,167
INSURANCE EXPENSES
Loss and settlement expenses									83,822	85,027	71,350
Policy acquisition costs									51,830	51,070	54,167
Other insurance expenses									12,725	14,108	13,819
NET EARNINGS
Net underwriting income									884	(11,859)	12,832
Surety segment
REVENUES
Net premiums earned									118,633	120,988	121,598
INSURANCE EXPENSES
Loss and settlement expenses									14,608	10,878	18,521
Policy acquisition costs									64,901	65,310	66,879
Other insurance expenses									9,516	10,001	9,234
NET EARNINGS
Net underwriting income									$ 29,608	$ 34,799	$ 26,964