OPERATING SEGMENT INFORMATION - Summary of Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
REVENUES
Net premiums earned	$ 215,626	$ 211,255	$ 207,541	$ 204,689	$ 204,002	$ 200,815	$ 196,522	$ 190,027	$ 839,111	$ 791,366	$ 737,937
Net investment income	17,775	17,532	16,998	16,565	16,962	16,314	14,577	14,232	68,870	62,085	54,876
Net realized gains	477	3,211	4,764	9,068	15,507	18,647	20,849	8,404	17,520	63,407	4,411
Net unrealized gains (losses) on equity securities	30,876	4,906	8,810	33,498	(64,200)	4,848	(12,611)	(26,772)	78,090	(98,735)
Consolidated revenue									1,003,591	818,123	797,224
INSURANCE EXPENSES
Loss and settlement expenses									413,416	428,193	401,584
Policy acquisition costs									288,697	267,738	252,515
Other insurance expenses									69,430	53,803	56,994
Insurance expenses									771,543	749,734	711,093
NET EARNINGS
Net underwriting income									67,568	41,632	26,844
Net investment income	17,775	17,532	16,998	16,565	16,962	16,314	14,577	14,232	68,870	62,085	54,876
Net realized gains	477	3,211	4,764	9,068	15,507	18,647	20,849	8,404	17,520	63,407	4,411
Net unrealized gains (losses) on equity securities	30,876	4,906	8,810	33,498	(64,200)	4,848	(12,611)	(26,772)	78,090	(98,735)
General corporate expense and interest on debt									(20,274)	(16,864)	(18,766)
Equity in earnings of unconsolidated investees									20,960	16,056	17,224
Earnings before income taxes	63,218	38,947	48,828	81,741	(32,708)	46,349	39,562	14,378	232,734	67,581	84,589
Income tax expense									41,092	3,402	(20,439)
Net earnings	$ 53,378	$ 32,324	$ 40,467	$ 65,473	$ (20,660)	$ 39,372	$ 33,251	$ 12,216	$ 191,642	64,179	105,028
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									$ 558,458	523,472	478,603
INSURANCE EXPENSES
Loss and settlement expenses									330,156	329,763	305,679
Policy acquisition costs									166,499	151,007	136,135
Other insurance expenses									41,202	31,562	32,885
NET EARNINGS
Net underwriting income									20,601	11,140	3,904
Property segment
REVENUES
Net premiums earned									164,022	149,261	138,346
INSURANCE EXPENSES
Loss and settlement expenses									73,614	83,822	85,027
Policy acquisition costs									55,986	51,830	51,070
Other insurance expenses									16,279	12,725	14,108
NET EARNINGS
Net underwriting income									18,143	884	(11,859)
Surety segment
REVENUES
Net premiums earned									116,631	118,633	120,988
INSURANCE EXPENSES
Loss and settlement expenses									9,646	14,608	10,878
Policy acquisition costs									66,212	64,901	65,310
Other insurance expenses									11,949	9,516	10,001
NET EARNINGS
Net underwriting income									$ 28,824	$ 29,608	$ 34,799