OPERATING SEGMENT INFORMATION - Summary of Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Mar. 04, 2015	Feb. 05, 2014
REVENUES
Net premiums earned	$ 179,371	$ 179,448	$ 172,339	$ 169,003	$ 179,892	$ 177,747	$ 168,604	$ 161,132	$ 700,161	$ 687,375	$ 630,802
Net investment income	13,754	13,964	13,431	13,495	13,844	14,200	13,982	13,582	54,644	55,608	52,763
Net realized gains	14,207	7,534	4,802	13,286	9,542	5,708	10,431	6,501	39,829	32,182	22,036
Consolidated revenue									794,634	775,165	705,601
INSURANCE EXPENSES
Loss and settlement expenses									299,045	296,609	259,801
Policy acquisition costs									241,078	229,283	210,651
Other insurance expenses									51,480	54,464	53,557
Insurance expenses									591,603	580,356	524,009
NET EARNINGS (LOSSES)
Net underwriting income									108,558	107,019	106,793
Net investment income	13,754	13,964	13,431	13,495	13,844	14,200	13,982	13,582	54,644	55,608	52,763
Net realized gains	14,207	7,534	4,802	13,286	9,542	5,708	10,431	6,501	39,829	32,182	22,036
General corporate expense and interest on debt									(17,263)	(17,660)	(16,841)
Equity in earnings of unconsolidated investees									10,914	12,338	10,915
Earnings before income taxes	45,582	51,937	54,650	44,513	46,479	48,594	52,423	41,991	196,682	189,487	175,666
Income tax expense									59,138	54,042	49,411
Net earnings	$ 33,853	$ 35,908	$ 37,185	$ 30,598	$ 37,497	$ 33,254	$ 35,725	$ 28,969	137,544	135,445	126,255
Facultative Reinsurance
Segment reporting information
Premiums Written, Gross									$ 3,500	5,900	9,100
Maui Jim Inc.
Segment reporting information
Ownership percentage	40.00%								40.00%
NET EARNINGS (LOSSES)
Equity in earnings of unconsolidated investees									$ 9,900	12,000	10,900
Prime Holdings Insurance Services, Inc. (Prime)
Segment reporting information
Ownership percentage	27.00%								27.00%			27.00%	20.00%
NET EARNINGS (LOSSES)
Equity in earnings of unconsolidated investees									$ 1,000	300
Casualty segment
REVENUES
Net premiums earned									412,248	382,105	324,022
INSURANCE EXPENSES
Loss and settlement expenses									218,414	199,133	148,860
Policy acquisition costs									119,529	108,747	93,463
Other insurance expenses									28,042	28,284	26,107
NET EARNINGS (LOSSES)
Net underwriting income									46,263	45,941	55,592
Property segment
REVENUES
Net premiums earned									170,924	197,776	200,141
INSURANCE EXPENSES
Loss and settlement expenses									69,851	89,589	96,271
Policy acquisition costs									57,214	58,646	58,650
Other insurance expenses									14,834	16,623	17,616
NET EARNINGS (LOSSES)
Net underwriting income									29,025	32,918	27,604
Surety segment
REVENUES
Net premiums earned									116,989	107,494	106,639
INSURANCE EXPENSES
Loss and settlement expenses									10,780	7,887	14,670
Policy acquisition costs									64,335	61,890	58,538
Other insurance expenses									8,604	9,557	9,834
NET EARNINGS (LOSSES)
Net underwriting income									$ 33,270	$ 28,160	$ 23,597