STOCKHOLDERS' EQUITY - Stock Option Activity (Details) - Stock Options - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock Option Activity [Abstract]
Outstanding at beginning of year (in shares)	951	887	946
Granted (in shares)	174	197	148
Exercised (in shares)	(256)	(112)	(198)
Forfeited (in shares)	(11)	(17)	(6)
Cancelled (in shares)	0	(4)	(3)
Outstanding at end of year (in shares)	858	951	887
Exercisable at end of year (in shares)	494	581	490
Weighted Average Exercise Price [Abstract]
Outstanding at beginning of year (in dollars per share)	$ 68.18	$ 61.59	$ 55.44
Granted (in dollars per share)	111.75	85.13	74.57
Exercised (in dollars per share)	55.26	43.67	41.71
Forfeited (in dollars per share)	92.94	80.88	74.90
Cancelled (in dollars per share)	0	70.90	48.54
Outstanding at end of year (in dollars per share)	80.58	68.18	61.59
Exercisable at end of period (in dollars per share)	$ 69.04	$ 59.29	$ 50.50
Aggregate intrinsic value for outstanding stock options	$ 29,735	$ 31,814	$ 16,192
Weighted average remaining contractual term for outstanding stock options	6 years 8 months 12 days
Aggregate intrinsic value for exercisable stock options outstanding	$ 22,805
Weighted average remaining contractual term for exercisable stock options outstanding	5 years 4 months 24 days
Weighted-average fair value of options granted (in dollars per share)	$ 24.36	$ 18.51	$ 18.62
Total intrinsic value of stock options exercised	$ 12,698	$ 6,135	$ 10,456