SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Investment in Unconsolidated Investees (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
INVESTMENT IN UNCONSOLIDATED INVESTEES:
Investment amount	$ 103,836,000				$ 94,967,000				$ 103,836,000	$ 94,967,000
Investee earnings recorded in income									20,960,000	16,056,000	$ 17,224,000
Reinsurance assumed									25,047,000	48,303,000	37,159,000
Net premiums earned	$ 215,626,000	$ 211,255,000	$ 207,541,000	$ 204,689,000	204,002,000	$ 200,815,000	$ 196,522,000	$ 190,027,000	839,111,000	791,366,000	737,937,000
Additional summarized financial information for investee
Dividends received									$ 13,200,000	9,900,000	0
Maui Jim Inc.
INVESTMENT IN UNCONSOLIDATED INVESTEES:
Equity ownership interest (as a percent)	40.00%								40.00%
Prime Holdings Insurance Services, Inc. (Prime)
INVESTMENT IN UNCONSOLIDATED INVESTEES:
Equity ownership interest (as a percent)	23.00%								23.00%
Maui Jim Inc.
INVESTMENT IN UNCONSOLIDATED INVESTEES:
Investment amount	$ 79,600,000				79,500,000				$ 79,600,000	79,500,000
Investee earnings recorded in income									13,600,000	12,500,000	14,400,000
Total investee net income									$ 35,600,000	30,300,000	34,400,000
Equity ownership interest (as a percent)	40.00%								40.00%
Additional summarized financial information for investee
Total assets	$ 282,200,000				265,600,000				$ 282,200,000	265,600,000
Total liabilities	104,800,000				90,400,000				104,800,000	90,400,000
Total equity	177,400,000				175,200,000				177,400,000	175,200,000
Undistributed earnings included in retained earnings	69,300,000								69,300,000
Dividends received									13,200,000	9,900,000	0
Prime Holdings Insurance Services, Inc. (Prime)
INVESTMENT IN UNCONSOLIDATED INVESTEES:
Investment amount	$ 24,200,000				$ 15,400,000				24,200,000	15,400,000
Investee earnings recorded in income									$ 7,400,000	3,600,000	2,800,000
Number of insurance carriers Company writes through | item									2
Equity ownership interest (as a percent)	23.00%								23.00%
Reinsurance assumed									$ 13,100,000	41,100,000	29,600,000
Net premiums earned									$ 28,700,000	$ 34,200,000	$ 21,000,000.0