OPERATING SEGMENT INFORMATION - Summary of Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
REVENUES
Net premiums earned	$ 188,296	$ 182,025	$ 184,331	$ 183,285	$ 187,869	$ 183,595	$ 180,226	$ 176,918	$ 737,937	$ 728,608	$ 700,161
Net investment income	14,446	14,187	13,238	13,005	13,153	13,504	13,048	13,370	54,876	53,075	54,644
Net realized gains (losses)	5,111	35	(1,359)	624	11,283	9,252	2,710	11,400	4,411	34,645	39,829
Consolidated revenue									797,224	816,328	794,634
INSURANCE EXPENSES
Loss and settlement expenses									401,584	349,778	299,045
Policy acquisition costs									252,515	249,612	241,078
Other insurance expenses									56,994	53,093	51,480
Insurance expenses									711,093	652,483	591,603
NET EARNINGS
Net underwriting income									26,844	76,125	108,558
Net investment income	14,446	14,187	13,238	13,005	13,153	13,504	13,048	13,370	54,876	53,075	54,644
Net realized gains (losses)	5,111	35	(1,359)	624	11,283	9,252	2,710	11,400	4,411	34,645	39,829
General corporate expense and interest on debt									(18,766)	(17,596)	(17,263)
Equity in earnings of unconsolidated investees									17,224	10,833	10,914
Earnings (loss) before income taxes	24,972	(862)	34,036	26,443	38,006	31,142	42,341	45,593	84,589	157,082	196,682
Income tax expense									(20,439)	42,162	59,138
Net earnings	$ 57,258	$ 1,734	$ 26,208	$ 19,828	$ 32,187	$ 22,263	$ 29,077	$ 31,393	105,028	114,920	137,544
PARENT COMPANY
REVENUES
Net investment income									647	942	810
Net realized gains (losses)									(36)	(360)	139
NET EARNINGS
Net investment income									647	942	810
Net realized gains (losses)									(36)	(360)	139
Equity in earnings of unconsolidated investees									14,436	9,764	9,893
Earnings (loss) before income taxes									(3,719)	(7,250)	(6,421)
Income tax expense									(16,601)	(8,467)	(5,499)
Net earnings									$ 105,028	114,920	137,544
Maui Jim Inc.
Segment reporting information
Ownership percentage	40.00%								40.00%
NET EARNINGS
Equity in earnings of unconsolidated investees									$ 14,400	9,700	9,900
Prime Holdings Insurance Services, Inc. (Prime)
Segment reporting information
Ownership percentage	23.00%								23.00%
NET EARNINGS
Equity in earnings of unconsolidated investees									$ 2,800	1,100	1,000
Casualty segment
REVENUES
Net premiums earned									478,603	454,843	412,248
INSURANCE EXPENSES
Loss and settlement expenses									305,679	259,907	218,414
Policy acquisition costs									136,135	128,566	119,529
Other insurance expenses									32,885	30,040	28,042
NET EARNINGS
Net underwriting income									3,904	36,329	46,263
Property segment
REVENUES
Net premiums earned									138,346	152,167	170,924
INSURANCE EXPENSES
Loss and settlement expenses									85,027	71,350	69,851
Policy acquisition costs									51,070	54,167	57,214
Other insurance expenses									14,108	13,819	14,834
NET EARNINGS
Net underwriting income									(11,859)	12,832	29,025
Surety segment
REVENUES
Net premiums earned									120,988	121,598	116,989
INSURANCE EXPENSES
Loss and settlement expenses									10,878	18,521	10,780
Policy acquisition costs									65,310	66,879	64,335
Other insurance expenses									10,001	9,234	8,604
NET EARNINGS
Net underwriting income									$ 34,799	$ 26,964	$ 33,270