STOCK-BASED COMPENSATION Performance-based Awards and Restricted Stock Units (Details) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2020 USD ($) $ / shares shares
Restricted Stock Units (RSUs)
Shares
Outstanding at January 1, 2020	860,000
Granted	70,000
Vested	(117,000)
Forfeited	(3,000)
Outstanding at March 31, 2020	810,000
Outstanding and expected to vest at March 31, 2020	752,000
Weighted- Average Grant Date Fair Value Per Share (in dollars per share)
Outstanding at January 1, 2020 \| $ / shares	$ 62.66
Granted \| $ / shares	97.97
Vested \| $ / shares	58.12
Forfeited \| $ / shares	64.40
Outstanding at March 31, 2020 \| $ / shares	$ 66.39
Weighted-Average Remaining Contractual Term (In years)
Outstanding at March 31, 2020	2 years 7 days
Outstanding and expected to vest at March 31, 2020	1 year 6 months 18 days
Aggregate Intrinsic Value (In thousands)
Outstanding at March 31, 2020 \| $	$ 71,528
Outstanding and expected to vest at March 31, 2020 \| $	$ 66,443
Long-Term Performance-Based Awards (PRSUs)
Shares
Outstanding at January 1, 2020	144,000
Granted	73,000
Vested	0
Forfeited	0
Outstanding at March 31, 2020	217,000
Outstanding and expected to vest at March 31, 2020	131,000
Weighted- Average Grant Date Fair Value Per Share (in dollars per share)
Outstanding at January 1, 2020 \| $ / shares	$ 64.05
Granted \| $ / shares	98.75
Vested \| $ / shares	0
Forfeited \| $ / shares	0
Outstanding at March 31, 2020 \| $ / shares	$ 75.70
Weighted-Average Remaining Contractual Term (In years)
Outstanding at March 31, 2020	1 year 9 months
Outstanding and expected to vest at March 31, 2020	2 years 3 months 18 days
Aggregate Intrinsic Value (In thousands)
Outstanding at March 31, 2020 \| $	$ 19,097
Outstanding and expected to vest at March 31, 2020 \| $	$ 11,564
Performance Based Awards (PSUs)
Shares
Outstanding at January 1, 2020	61,000
Granted	42,000
Vested	(61,000)
Forfeited	0
Outstanding at March 31, 2020	42,000
Outstanding and expected to vest at March 31, 2020	42,000
Weighted- Average Grant Date Fair Value Per Share (in dollars per share)
Outstanding at January 1, 2020 \| $ / shares	$ 70.11
Granted \| $ / shares	100.23
Vested \| $ / shares	70.11
Forfeited \| $ / shares	0
Outstanding at March 31, 2020 \| $ / shares	$ 100.23
Weighted-Average Remaining Contractual Term (In years)
Outstanding at March 31, 2020	9 months
Outstanding and expected to vest at March 31, 2020	9 months
Aggregate Intrinsic Value (In thousands)
Outstanding at March 31, 2020 \| $	$ 3,728
Outstanding and expected to vest at March 31, 2020 \| $	$ 3,728
Minimum [Member] \| Long-Term Performance-Based Awards (PRSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Performance Based Awards Shares Released As Percentage Of Target Number	0.00%
Minimum [Member] \| Performance Based Awards (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Performance Based Awards Shares Released As Percentage Of Target Number	0.00%
Maximum [Member] \| Long-Term Performance-Based Awards (PRSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Performance Based Awards Shares Released As Percentage Of Target Number	200.00%
Maximum [Member] \| Performance Based Awards (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Performance Based Awards Shares Released As Percentage Of Target Number	200.00%

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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