Summary of Significant Accounting Policies ((Weighted-average assumptions) (Details)
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12 Months Ended |
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
| Stock Option |
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| Assumptions used to estimate the fair value of stock options |
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| Expected term (in years) |
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6 years 29 days
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| Expected volatility, minimum (as a percent) |
45.00%
|
52.00%
|
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| Expected volatility, maximum (as a percent) |
52.00%
|
57.00%
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|
| Expected volatility (as a percent) |
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|
56.00%
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| Risk-free interest rate, minimum (as a percent) |
1.48%
|
1.71%
|
1.00%
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| Risk-free interest rate, maximum (as a percent) |
1.92%
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2.00%
|
1.76%
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| Stock Option | Minimum |
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| Assumptions used to estimate the fair value of stock options |
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|
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| Expected term (in years) |
5 years 3 months 7 days
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5 years 9 months 7 days
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| Stock Option | Maximum |
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| Assumptions used to estimate the fair value of stock options |
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|
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| Expected term (in years) |
6 years 29 days
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6 years 29 days
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| Employee Stock Purchase Plan |
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| Assumptions used to estimate the fair value of stock options |
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|
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| Expected volatility, minimum (as a percent) |
42.00%
|
43.00%
|
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| Expected volatility, maximum (as a percent) |
44.00%
|
44.00%
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|
| Risk-free interest rate, minimum (as a percent) |
0.08%
|
0.08%
|
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| Risk-free interest rate, maximum (as a percent) |
0.71%
|
0.49%
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| Employee Stock Purchase Plan | Minimum |
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| Assumptions used to estimate the fair value of stock options |
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|
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| Expected term (in years) |
6 months
|
7 months 17 days
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| Employee Stock Purchase Plan | Maximum |
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| Assumptions used to estimate the fair value of stock options |
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|
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| Expected term (in years) |
2 years 1 month 6 days
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2 years 1 month 21 days
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