Aggregate number of common shares reserved for future issuance.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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- Definition

Number of shares issued during the period as a result of an employee stock purchase plan.

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Aggregate change in value for stock issued during the period as a result of employee stock purchase plan.

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SHARE-BASED COMPENSATION - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Apr. 30, 2019	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance	6,500,000		28,450,000	24,450,000
Options exercisable, number of shares	4,700,000
Options exercisable, weighted-average exercise price (usd per share)	$ 178.62
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance	2,800,000
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock Purchase Plan, number of shares purchased by employees	100,000	100,000
Employee Stock Purchase Plan, value of shares purchased by employees	$ 30.3	$ 25.3