STOCK-BASED COMPENSATION Performance-based Awards and Restricted Stock Units (Details) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2019 USD ($) $ / shares shares
Restricted Stock Units (RSUs)
Shares
Outstanding at January 1, 2019	895,000
Granted	263,000
Vested	(290,000)
Forfeited	(12,000)
Outstanding at June 30, 2019	856,000
Outstanding and expected to vest at June 30, 2019	780,000
Weighted- Average Grant Date Fair Value Per Share (in dollars per share)
Outstanding at January 1, 2019 \| $ / shares	$ 58.19
Granted \| $ / shares	68.37
Vested \| $ / shares	56.15
Forfeited \| $ / shares	60.25
Outstanding at June 30, 2019 \| $ / shares	$ 61.98
Weighted-Average Remaining Contractual Term (In years)
Outstanding at June 30, 2019	2 years 21 days
Outstanding and expected to vest at June 30, 2019	1 year 11 months 19 days
Aggregate Intrinsic Value (In thousands)
Outstanding at June 30, 2019 \| $	$ 68,664
Outstanding and expected to vest at June 30, 2019 \| $	$ 62,565
Long-Term Performance-Based Awards (PRSUs)
Shares
Outstanding at January 1, 2019	213,000
Granted	72,000
Vested	(70,000)
Forfeited	0
Outstanding at June 30, 2019	215,000
Outstanding and expected to vest at June 30, 2019	86,000
Weighted- Average Grant Date Fair Value Per Share (in dollars per share)
Outstanding at January 1, 2019 \| $ / shares	$ 55.48
Granted \| $ / shares	68.17
Vested \| $ / shares	43.26
Forfeited \| $ / shares	0
Outstanding at June 30, 2019 \| $ / shares	$ 63.70
Weighted-Average Remaining Contractual Term (In years)
Outstanding at June 30, 2019	1 year 6 months
Outstanding and expected to vest at June 30, 2019	2 years 3 months 14 days
Aggregate Intrinsic Value (In thousands)
Outstanding at June 30, 2019 \| $	$ 17,223
Outstanding and expected to vest at June 30, 2019 \| $	$ 6,920
Performance Based Awards (PSUs)
Shares
Outstanding at January 1, 2019	26,000
Granted	92,000
Vested	(26,000)
Forfeited	0
Outstanding at June 30, 2019	92,000
Outstanding and expected to vest at June 30, 2019	42,000
Weighted- Average Grant Date Fair Value Per Share (in dollars per share)
Outstanding at January 1, 2019 \| $ / shares	$ 62.87
Granted \| $ / shares	70.08
Vested \| $ / shares	62.87
Forfeited \| $ / shares	0
Outstanding at June 30, 2019 \| $ / shares	$ 70.08
Weighted-Average Remaining Contractual Term (In years)
Outstanding at June 30, 2019	6 months
Outstanding and expected to vest at June 30, 2019	6 months
Aggregate Intrinsic Value (In thousands)
Outstanding at June 30, 2019 \| $	$ 7,406
Outstanding and expected to vest at June 30, 2019 \| $	$ 3,340
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 number of grants made 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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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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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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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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