STOCK-BASED COMPENSATION - RSA activity (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 17, 2020	May 31, 2020	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Award expiration period	10 years
Allocated share-based compensation expense				$ 12.8	$ 9.1	$ 6.7
Arthur Przybyl [Member]
Options, nonvested (in shares)		63,305
Options, vested (in shares)		101,376
Allocated share-based compensation expense			$ 3.4	$ 3.4
Restricted Stock [Member]
Unvested, Shares, Outstanding, Beginning of period				192,000	117,000	85,000
Unvested Shares, Granted				305,000	122,000	65,000
Unvested Shares, Vested				(127,000)	(42,000)	(33,000)
Unvested Shares, Forfeited				(18,000)	(5,000)
Unvested Shares, Outstanding, End of period				352,000	192,000	117,000	85,000
Weighted Average Grant Date Fair Value, Outstanding, Beginning of period				$ 61.46	$ 54.04	$ 48.34
Weighted Average Grant Date Fair Value, Granted				44.42	66.39	58.11
Weighted Average Grant Date Fair Value, Vested				58.88	54.77	47.34
Weighted Average Grant Date Fair Value, Forfeited				51.53	62.63
Weighted Average Grant Date Fair Value, Outstanding, End of period				$ 48.14	$ 61.46	$ 54.04	$ 48.34
Weighted Average Remaining Term (years)				2 years 8 months 12 days	2 years 7 months 6 days	2 years 1 month 6 days	2 years 7 months 6 days
Unrecognized non-option costs				$ 12.6
Period of cost recognition				2 years 8 months 12 days
Restricted Stock [Member] | Employees and Consultants [Member]
Vesting period				4 years
Restricted Stock [Member] | Non Employee Director [Member]
Vesting period				1 year
Restricted Stock [Member] | Arthur Przybyl [Member]
Unvested Shares, Outstanding, End of period		48,448