STOCK-BASED COMPENSATION - Stock option activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock Options
Aggregate Intrinsic Value (in thousands)
Shares surrendered to satisfy exercise price and/or tax withholding requirements (in shares)	10,354	18,952	142,752
Stock Incentive Plan
Option Shares Outstanding
Outstanding, beginning of period (in shares)	1,437,460	1,443,733	1,581,699
Granted (in shares)	450,000	54,500	203,000
Exercise of stock options (in shares)	(53,214)	(60,773)	(337,428)
Forfeited (in shares)	(1,000)	0	(3,538)
Outstanding, end of period (in shares)	1,833,246	1,437,460	1,443,733
Exercisable (in shares)	1,025,846
Weighted Average Exercise Price
Outstanding, beginning of period (in dollars per share)	$ 50.47	$ 48.75	$ 40.77
Granted (in dollars per share)	77.99	69.44	69.69
Exercise of stock options (in dollars per share)	34.40	26.51	24.15
Forfeited (in dollars per share)	48.85	0	27.43
Outstanding, end of period (in dollars per share)	57.69	$ 50.47	$ 48.75
Exercisable (in dollars per share)	$ 48.30
Weighted Average Remaining Life (Years)
Outstanding	6 years 7 months 6 days	6 years 7 months 6 days	7 years 4 months 24 days
Exercisable	5 years 4 months 24 days
Aggregate Intrinsic Value (in thousands)
Outstanding	$ 51,426	$ 23,840	$ 36,428
Exercisable	$ 38,410