STOCK-BASED COMPENSATION - Stock option and restricted stock option activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Option Shares
Treasury Stock, Common, Value	$ 723	$ 659
Options [Member]
Option Shares
Outstanding at the beginning of the period (in shares)	759	767	578
Granted (in shares)	160	156	207
Options Exercised/RSAs Vested (in shares)	(130)	(142)	(13)
Forfeited (in shares)	(31)	(18)	(5)
Expired (in shares)	(1)	(4)	0
Outstanding at the end of the period (in shares)	757	759	767	578
Exercisable at the end of the period (in shares)	366
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 49.74	$ 42.93	$ 39.28
Granted (in dollars per share)	65.97	57.60	51.66
Exercised (in dollars per share)	41.99	19.47	15.92
Forfeited (in dollars per share)	56.66	60.17	53.29
Expired (in dollars per share)	54.36	74.53	0.00
Outstanding at the end of the period (in dollars per share)	54.21	49.74	42.93	$ 39.28
Exercisable at the end of the period (in dollars per share)	50.47
Weighted Average Grant-date Fair Value
Granted (in dollars per share)	$ 40.14	$ 31.76	$ 27.04
Weighted Average Remaining Term (years)
Outstanding at the end of the period weighted average remaining term	7 years 2 months 12 days	7 years 7 months 6 days	7 years 9 months 18 days	8 years 2 months 12 days
Exercisable at the end of the period weighted average remaining term	6 years 2 months 12 days
Aggregate Intrinsic Value
Outstanding at the beginning of the period intrinsic value (in dollars)	$ 2,221	$ 16,785	$ 12,928
Exercised at the end of the period intrinsic value (in dollars)	3,335	5,863	542
Outstanding at the end of the period intrinsic value (in dollars)	6,761	$ 2,221	$ 16,785	$ 12,928
Exercisable at the end of the period intrinsic value (in dollars)	$ 4,469