STOCKHOLDERS' EQUITY - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2020
Number of Stock Options Outstanding
Beginning balance (in shares)	23,619,804
Exercised (in shares)	(3,396,568)
Forfeited (in shares)	(20,135)
Ending balance (in shares)	20,203,101	23,619,804
Weighted Average Exercise Price
Beginning balance (in USD per share)	$ 12.66
Exercised (in USD per share)	9.09
Forfeited (in USD per share)	71.99
Ending balance (in USD per share)	$ 12.66	$ 12.66	$ 10.25
Options Exercisable
Options exercisable (in shares)			18,862,499
Options exercisable (in USD per share)			$ 10.25
Additional Disclosures
Weighted average remaining contractual term, options outstanding	4 years 10 months 17 days	4 years 10 months 20 days
Weighted average remaining contractual term, options exercisable	4 years 4 months 24 days
Aggregate intrinsic value, options outstanding		$ 1,191,746	$ 811,454
Aggregate intrinsic value, options exercisable			$ 799,553

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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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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Number of share options (or share units) exercised during the current period.

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