N/A.

No definition available.

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The maximum fair market value of stock an employee can purchase under the plan per period.

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No definition available.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Aggregate number of common shares reserved for future issuance.

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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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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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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- Definition

The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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The highest quantity of shares an employee can purchase under the plan per period.

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- Definition

Number of shares authorized for issuance under share-based payment arrangement.

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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

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No definition available.

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STOCK-BASED COMPENSATION - Restricted stock activity (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	May 31, 2018	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee Stock Purchase Plan
Compensation expense		$ 4,600,000	$ 6,300,000	$ 12,900,000	$ 11,700,000
ESPP
Employee Stock Purchase Plan
Number of shares of common stock made available for purchase to employees	750,000
Maximum percentage of annual salary that an employee is permitted to utilize to purchase stock	10.00%
Maximum number of shares that a participant can purchase during any single offering period	312
Maximum fair market value of stock an employee can purchase under the plan per calendar year	$ 25,000
Compensation expense		$ 100,000	$ 100,000	$ 200,000	$ 200,000
Shares were reserved for future issuance		710,103		710,103
ESPP \| US
Employee Stock Purchase Plan
Exercise price per share of common stock as a percent of fair market value	90.00%
ESPP \| International
Employee Stock Purchase Plan
Exercise price per share of common stock as a percent of fair market value	85.00%
Restricted Stock and Restricted Stock Units
Number of shares
Beginning balance (in shares)				436,013
Granted (in shares)				183,731
Vested (in shares)				(268,187)
Forfeited (in shares)				(11,080)
Ending balance (in shares)		340,477		340,477
Weighted average grant date fair value
Beginning balance (in USD per share)				$ 92.47
Granted (in dollars per share)				117.43
Vested (in USD per share)				88.07
Forfeited (in USD per share)				105.47
Ending balance (in USD per share)		$ 108.98		$ 108.98
Performance-Based Restricted Stock Units
Number of shares
Beginning balance (in shares)				132,248
Granted (in shares)				72,975
Vested (in shares)		(48,053)		(48,053)
Forfeited (in shares)				(34,504)
Ending balance (in shares)		122,666		122,666
Weighted average grant date fair value
Beginning balance (in USD per share)				$ 105.75
Granted (in dollars per share)				125.62
Vested (in USD per share)				108.91
Forfeited (in USD per share)				109.85
Ending balance (in USD per share)		$ 115.18		$ 115.18