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Stock Incentive Plan (Tables) | 12 Months Ended
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Dec. 31, 2017
Stock Incentive Plan |
Schedule of weighted-average assumptions for options granted |
Year ended December 31, |  | 2017 |  | 2016 |  | 2015 |
Expected term (in years) |  | 6.16 |  | 4.60 |  | 4.00 |
Expected volatility |  | 50.43 | % | 59.58 | % | 69.08 | %
Risk free rate |  | 2.12 | % | 1.72 | % | 1.40 | %
Expected dividends |  | — | % | — | % | — | %
Summary of stock option activity |
|  |  |  |  |  | Weighted |
|  |  |  |  |  | Average |
|  |  |  | Weighted |  | Remaining |
|  |  |  | Average |  | Contractual |
|  | Stock Awards |  | Exercise Price |  | Term(Years) |
Outstanding at December 31, 2014: |  | 2,743,818 |  | 3.03 |  | 5.94 |
Granted |  | 946,250 |  | 4.31 |  |  |
Forfeited |  | (290,478) |  | (3.12) |  |  |
Exercised |  | (171,563) |  | (2.99) |  |  |
Outstanding at December 31, 2015: |  | 3,228,027 |  | 3.40 |  | 5.43 |
Granted |  | 1,529,850 |  | 7.67 |  |  |
Forfeited |  | (75,938) |  | (3.74) |  |  |
Exercised |  | (340,942) |  | (3.16) |  |  |
Outstanding at December 31, 2016: |  | 4,340,997 |  | 4.92 |  | 5.93 |
Granted |  | 1,298,355 |  | 19.99 |  |  |
Forfeited |  | (94,777) |  | (6.29) |  |  |
Exercised |  | (568,135) |  | (3.43) |  |  |
Outstanding at December 31, 2017 |  | 4,976,440 |  | 8.99 |  | 6.39 |
Exercisable at December 31, 2017 |  | 2,343,796 |  | 4.12 |  | 4.26 |
Schedule of non-vested share-based payment activity with employees |
|  |  |  | Weighted Average |
|  | Number of Awards |  | Exercise Price |
Nonvested options - December 31, 2014: |  | 1,159,486 |  | 3.37 |
Granted |  | 946,250 |  | 4.31 |
Vested |  | (635,289) |  | (3.32) |
Forfeited |  | (290,478) |  | (3.12) |
Nonvested options - December 31, 2015: |  | 1,179,969 |  | 4.21 |
Granted |  | 1,529,850 |  | 7.67 |
Vested |  | (512,562) |  | (4.21) |
Forfeited |  | (75,938) |  | (3.74) |
Nonvested options - December 31, 2016: |  | 2,121,319 |  | 6.72 |
Granted |  | 1,298,355 |  | 19.99 |
Vested |  | (692,253) |  | (6.49) |
Forfeited |  | (94,777) |  | (6.29) |
Nonvested options - December 31, 2017: |  | 2,632,644 |  | 13.33 |

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- Definition Tabular disclosure of the number and weighted-average exercise prices (or conversion ratios) for share options (or share units) that were outstanding at the beginning and end of the year, vested and expected to vest, exercisable or convertible at the end of the year, and the number of share options or share units that were granted, exercised or converted, forfeited, and expired during the year. + 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 (c)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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