COMPENSATION PLANS - Summary of Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding beginning of year (in shares)	545,000	548,000	288,000
Granted during the year (in shares)	0	0	340,000
Forfeited during the year (in shares)	0	0	0
Exercised during the year (in shares)	(9,000)	(3,000)	(80,000)
Outstanding, end of year (in shares)	536,000	545,000	548,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding beginning of year (in dollars per share)	$ 44.35	$ 44.07	$ 23.59
Granted during the year (in dollars per share)	0	0	53.83
Forfeited during the period (in dollars per share)	0	0	0
Exercised during the year (in dollars per share)	0.67	0.78	11.62
Outstanding, end of year (in dollars per share)	$ 45.11	$ 44.35	$ 44.07
Vested Options:
Vested during the year (in shares)	115,000	115,000	30,000
Vested during the year (in dollars per share)	$ 50.46	$ 50.46	$ 40.95
Eligible, end of year for exercise (in shares)	336,000	230,000	118,000
Eligible, end of year for exercise (in dollars per share)	$ 41.07	$ 34.72	$ 18.36
Aggregate intrinsic value ($ in thousands):
Total options outstanding	$ 4,398	$ 1,570	$ 13,932
Options exercisable	4,051	1,570	6,037
Options exercised	$ 381	$ 195	$ 2,601
Weighted average fair value of options granted during the year (in dollars per share)			$ 17.76
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding beginning of year (in shares)	535,000	535,000	270,000
Granted during the year (in shares)	0	0	340,000
Forfeited during the year (in shares)	0	0	0
Exercised during the year (in shares)	0	0	(75,000)
Outstanding, end of year (in shares)	535,000	535,000	535,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding beginning of year (in dollars per share)	$ 54.53	$ 54.53	$ 32.29
Granted during the year (in dollars per share)	0	0	63.85
Forfeited during the period (in dollars per share)	0	0	0
Exercised during the year (in dollars per share)	0	0	16.50
Outstanding, end of year (in dollars per share)	$ 54.53	$ 54.53	$ 54.53
Vested Options:
Vested during the year (in shares)	115,000	115,000	30,000
Vested during the year (in dollars per share)	$ 60.71	$ 60.71	$ 51.87
Eligible, end of year for exercise (in shares)	336,000	220,000	105,000
Eligible, end of year for exercise (in dollars per share)	$ 50.04	$ 44.46	$ 26.66
Aggregate intrinsic value ($ in thousands):
Total options outstanding	$ 3,190	$ 983	$ 8,458
Options exercisable	3,066	983	4,521
Options exercised	$ 0	$ 0	$ 3,822
Weighted average fair value of options granted during the year (in dollars per share)			$ 14.66

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Number of options outstanding, including both vested and non-vested options.

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