Stock-Based Compensation - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($) item $ / shares shares
Stock-based compensation
Number of stock plans \| item	4
Number of Shares Underlying Options
Outstanding at beginning of period (in shares) \| shares	7,026
Granted (in shares) \| shares	743
Exercised (in shares) \| shares	(144)
Canceled/forfeited/expired (in shares) \| shares	(146)
Outstanding at end of period (in shares) \| shares	7,479
Vested and expected to vest at end of period (in shares) \| shares	7,324
Exercisable at end of period (in shares) \| shares	4,083
Weighted Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 21.36
Granted (in dollars per share)	30.92
Exercised (in dollars per share)	10.14
Canceled/forfeited/expired (in dollars per share)	29.03
Outstanding at end of period (in dollars per share)	22.37
Vested and expected to vest at end of period (in dollars per share)	22.16
Exercisable at end of period (in dollars per share)	13.88
Additional disclosures
Weighted average estimated grant date fair value of options granted (in dollars per share)	$ 14.46
Weighted average estimated grant date fair value of options granted \| $	$ 9.3
Unamortized stock-based compensation expense \| $	$ 53.7
Weighted Average Remaining Contractual Life	3 years
First anniversary \| RSU
Stock-based compensation
Vesting (as a percent)	25.00%
Second anniversary \| RSU
Stock-based compensation
Vesting (as a percent)	25.00%
Third anniversary \| RSU
Stock-based compensation
Vesting (as a percent)	25.00%
Fourth anniversary \| RSU
Stock-based compensation
Vesting (as a percent)	25.00%

The unamortized stock-based compensation expense of options.

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Represents the number of stock-based compensation plans.

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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

For presentations that combine terminations, 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 or that expired.

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

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- Definition

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

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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- Definition

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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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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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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- Definition

Percentage of vesting of share-based compensation awards.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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