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Net (Loss) Income per Share Attributable to Common Stock - Anti-Dilutive Awards Excluded from Calculation (Details) - Weighted Average - shares | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Anti-dilutive Securities Excluded from Calculation of Earnings Per Share |  |  |
Weighted average number of securities excluded from calculation | 743,872 | 756,527 | 552,577
Stock options |  |  |
Anti-dilutive Securities Excluded from Calculation of Earnings Per Share |  |  |
Weighted average number of securities excluded from calculation | 338,355 | 411,763 | 425,981
Restricted stock units |  |  |
Anti-dilutive Securities Excluded from Calculation of Earnings Per Share |  |  |
Weighted average number of securities excluded from calculation | 332,221 | 268,461 | 126,596
Non-participating restricted stock awards |  |  |
Anti-dilutive Securities Excluded from Calculation of Earnings Per Share |  |  |
Weighted average number of securities excluded from calculation | 73,296 | 76,303 |

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- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
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