Stock-Based Compensation - Options Activity (Details) shares in Thousands	3 Months Ended
Mar. 31, 2019 $ / shares shares
Shares (in thousands)
Options outstanding, beginning of period (in shares) \| shares	3,744
Granted (in shares) \| shares	770
Exercised (in shares) \| shares	(349)
Canceled (in shares) \| shares	(10)
Options outstanding, end of period (in shares) \| shares	4,155
Weighted- Average Exercise Price per Share
Outstanding weighted average exercise price, beginning balance (in usd per share) \| $ / shares	$ 20.69
Granted weighted average exercise price (in usd per share \| $ / shares	51.86
Exercised weighted average exercise price (in usd per share \| $ / shares	15.17
Canceled weighted average exercise price (in usd per share \| $ / shares	29.94
Outstanding weighted average exercise price, ending balance (in usd per share \| $ / shares	$ 26.91

Weighted average price of options that were either forfeited or expired.

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- Definition

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested 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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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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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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

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