Stock-Based Compensation (Summary of Option Activity) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning Balance, Outstanding, Number of Options	10,371,472
Granted, Number of Options	251,021
Exercised, Number of Options	(367,421)
Forfeited, Number of Options	(136,444)
Expired, Number of Options	(13,451)
Ending Balance, Outstanding, Number of Options	10,105,177
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning Balance, Outstanding, Weighted-Average Exercise Price	$ 4.59
Granted, Weighted-Average Exercise Price	$ 19.73
Exercised, Weighted-Average Exercise Price	$ 1.00
Forfeited, Weighted-Average Exercise Price	$ 3.55
Expired, Weighted-Average Exercise Price	$ 0.65
Ending Balance, Outstanding, Weighted-Average Exercise Price	$ 5.11
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, Weighted-Average Remaining Contractual Term	8 years 3 months 7 days
Outstanding, Aggregate Intrinsic Value	$ 165,086
Exercisable, Number of Options	3,279,655
Exercisable, Weighted-Average Exercise Price	$ 0.82
Exercisable, Weighted-Average Remaining Contractual Term	7 years 2 months 23 days
Exercisable, Aggregate Intrinsic Value	67,902
Vested or expected to vest, Number of Options	9,440,461
Vested or expected to vest, Weighted-Average Exercise Price	$ 4.87
Vested or expected to vest, Weighted-Average Remaining Contractual Term	8 years 4 months 10 days
Vested or expected to vest, Aggregate Intrinsic Value	$ 157,175

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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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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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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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

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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 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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Amount by which the current fair value of the underlying stock exceeds the exercise price of fully vested and expected to vest options outstanding.

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As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

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As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

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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 price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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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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