STOCK-BASED COMPENSATION Performance-based Awards and Restricted Stock Units (Details) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($) $ / shares shares
Performance Based Awards (PSUs)
Shares
Outstanding at January 1, 2019	26,000
Granted	58,000
Vested	(26,000)
Forfeited	0
Outstanding at March 31, 2019	58,000
Outstanding and expected to vest at March 31, 2019	38,000
Weighted- Average Grant Date Fair Value Per Share (in dollars per share)
Outstanding at January 1, 2019 \| $ / shares	$ 62.87
Granted \| $ / shares	69.46
Vested \| $ / shares	62.87
Forfeited \| $ / shares	0.00
Outstanding at March 31, 2019 \| $ / shares	$ 69.46
Weighted-Average Remaining Contractual Term (In years)
Outstanding at March 31, 2019	9 months
Outstanding and expected to vest at March 31, 2019	9 months
Aggregate Intrinsic Value (In thousands)
Outstanding at March 31, 2019 \| $	$ 4,043
Outstanding and expected to vest at March 31, 2019 \| $	$ 2,648
Long-Term Performance-Based Awards (PRSUs)
Shares
Outstanding at January 1, 2019	213,000
Granted	72,000
Vested	(70,000)
Forfeited	0
Outstanding at March 31, 2019	215,000
Outstanding and expected to vest at March 31, 2019	93,000
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	0.00
Outstanding at March 31, 2019 \| $ / shares	$ 63.70
Weighted-Average Remaining Contractual Term (In years)
Outstanding at March 31, 2019	1 year 9 months
Outstanding and expected to vest at March 31, 2019	2 years 4 months 27 days
Aggregate Intrinsic Value (In thousands)
Outstanding at March 31, 2019 \| $	$ 15,023
Outstanding and expected to vest at March 31, 2019 \| $	$ 6,534
Restricted Stock Units (RSUs)
Shares
Outstanding at January 1, 2019	895,000
Granted	119,000
Vested	(112,000)
Forfeited	(4,000)
Outstanding at March 31, 2019	898,000
Outstanding and expected to vest at March 31, 2019	827,000
Weighted- Average Grant Date Fair Value Per Share (in dollars per share)
Outstanding at January 1, 2019 \| $ / shares	$ 58.19
Granted \| $ / shares	67.51
Vested \| $ / shares	54.38
Forfeited \| $ / shares	56.81
Outstanding at March 31, 2019 \| $ / shares	$ 59.91
Weighted-Average Remaining Contractual Term (In years)
Outstanding at March 31, 2019	2 years 2 months 12 days
Outstanding and expected to vest at March 31, 2019	1 year 8 months 15 days
Aggregate Intrinsic Value (In thousands)
Outstanding at March 31, 2019 \| $	$ 62,796
Outstanding and expected to vest at March 31, 2019 \| $	$ 57,871
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%
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%
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%
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%

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Aggregate Intrinsic Value

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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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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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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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