STOCK-BASED COMPENSATION Performance-based Awards and Restricted Stock Units (Details) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($) $ / shares shares
Performance Based Awards (PSUs)
Shares
Outstanding at January 1, 2018	79
Granted	89
Vested	(79)
Forfeited	0
Outstanding at September 30, 2018	89
Outstanding and expected to vest at September 30, 2018	27
Weighted- Average Grant Date Fair Value Per Share (in dollars per share)
Outstanding at January 1, 2018 \| $ / shares	$ 63.99
Granted \| $ / shares	62.87
Vested \| $ / shares	63.99
Forfeited \| $ / shares	0.00
Outstanding at September 30, 2018 \| $ / shares	$ 62.87
Weighted-Average Remaining Contractual Term (In years)
Outstanding at September 30, 2018	3 months
Outstanding and expected to vest at September 30, 2018	3 months
Aggregate Intrinsic Value (In thousands)
Outstanding at September 30, 2018 \| $	$ 5,588
Outstanding and expected to vest at September 30, 2018 \| $	$ 1,677
Long-Term Performance-Based Awards (PRSUs)
Shares
Outstanding at January 1, 2018	184
Granted	72
Vested	(38)
Forfeited	0
Outstanding at September 30, 2018	218
Outstanding and expected to vest at September 30, 2018	161
Weighted- Average Grant Date Fair Value Per Share (in dollars per share)
Outstanding at January 1, 2018 \| $ / shares	$ 52.80
Granted \| $ / shares	59.90
Vested \| $ / shares	52.45
Forfeited \| $ / shares	0.00
Outstanding at September 30, 2018 \| $ / shares	$ 55.20
Weighted-Average Remaining Contractual Term (In years)
Outstanding at September 30, 2018	1 year 2 months 25 days
Outstanding and expected to vest at September 30, 2018	1 year 5 days
Aggregate Intrinsic Value (In thousands)
Outstanding at September 30, 2018 \| $	$ 13,752
Outstanding and expected to vest at September 30, 2018 \| $	$ 10,144
Restricted Stock Units (RSUs)
Shares
Outstanding at January 1, 2018	948
Granted	268
Vested	(288)
Forfeited	(23)
Outstanding at September 30, 2018	905
Outstanding and expected to vest at September 30, 2018	828
Weighted- Average Grant Date Fair Value Per Share (in dollars per share)
Outstanding at January 1, 2018 \| $ / shares	$ 55.51
Granted \| $ / shares	62.96
Vested \| $ / shares	53.77
Forfeited \| $ / shares	59.39
Outstanding at September 30, 2018 \| $ / shares	$ 58.17
Weighted-Average Remaining Contractual Term (In years)
Outstanding at September 30, 2018	1 year 11 months 22 days
Outstanding and expected to vest at September 30, 2018	1 year 10 months 10 days
Aggregate Intrinsic Value (In thousands)
Outstanding at September 30, 2018 \| $	$ 57,200
Outstanding and expected to vest at September 30, 2018 \| $	$ 52,347
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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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding and Expected to Vest, Aggregate Intrinsic Value

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Share Based Compensation Arrangement By Share Based Payment Award, Equity Instruments Other Than Options, Outstanding And Expected To Vest, Weighted Average Remaining Contractual Term in Years

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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- Definition

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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- Definition

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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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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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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-Publisher FASB
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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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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-Name Accounting Standards Codification
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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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