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Stock-Based Compensation (Assumptions Used in Estimation of Fair Value of Stock) (Details) - $ / shares | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Range of Black-Scholes fair values of ESPP shares granted | $ 1.88 | $ 4.38 | $ 2.39
Risk-free interest rate, minimum | 0.97% | 1.19% | 1.24%
Risk-free interest rate, maximum | 1.78% | 2.13% | 2.22%
Dividend yield | 0.00% | 0.00% | 0.00%
Volatility, minimum | 57.86% | 53.58% | 52.47%
Volatility, maximum | 108.88% | 68.39% | 67.93%
Employee Stock Purchase Plan [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Risk-free interest rate, minimum | 0.22% | 0.05% | 0.04%
Risk-free interest rate, maximum | 0.61% | 0.35% | 0.24%
Dividend yield | 0.00% | 0.00% | 0.00%
Volatility, minimum | 43.03% | 40.79% | 50.80%
Volatility, maximum | 86.75% | 64.24% | 67.57%
Expected forfeiture rate | 5.00% | 5.00% | 5.00%
Minimum [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Expected term (in years) | 4 years 2 months 19 days | 3 years 11 months 23 days | 4 years 14 days
Expected forfeiture rate | 0.00% | 0.00% | 0.00%
Minimum [Member] | Employee Stock Purchase Plan [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Range of Black-Scholes fair values of ESPP shares granted | $ 1.86 | $ 1.06 | $ 0.78
Expected term (in years) | 6 months | 6 months | 6 months
Maximum [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Expected term (in years) | 7 years 3 months 11 days | 7 years 4 months 2 days | 6 years 11 months 16 days
Expected forfeiture rate | 16.33% | 16.33% | 23.15%
Maximum [Member] | Employee Stock Purchase Plan [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Range of Black-Scholes fair values of ESPP shares granted | $ 4.76 | $ 3.38 | $ 2.08
Expected term (in years) | 2 years | 2 years | 1 year 6 months

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- Definition Estimated rate of forfeitures. + References No definition available. + Details
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References No definition available. + Details
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- Definition The estimated measure of the minimum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References No definition available. + Details
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- Definition The maximum risk-free interest rate assumption that is used in valuing an option on its own shares. + References No definition available. + Details
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- Definition The minimum risk-free interest rate assumption that is used in valuing an option on its own shares. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.D.2) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 + Details
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