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General & Administrative Expenses - Summary of activity for restricted stock awards (Details) - $ / shares | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Restricted common stock |  |  |  |
Outstanding beginning of period | 1,376,820 | 1,385,832 | 919,515 | 493,523
Outstanding end of period | 1,086,331 | 1,376,820 | 1,385,832 | 919,515
Granted | 900,000 | 824,000 | 850,000 | 750,000
Exercised* | 1,132,988 | 833,012 | 383,683 | 324,008
Forfeited | 57,501 |  |  |
Share options |  |  |  |
Outstanding | 310,000 | 310,000 | 310,000 | 310,965
Forfeited |  |  | 965 |
Weighted average exercise price ** |  |  |  |
Outstanding | $ 9.64 | $ 9.64 | $ 9.64 | $ 9.64

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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Number of non-option equity instruments forfeited. + References No definition available. + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans. + References No definition available. + Details
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- Definition Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan. + References No definition available. + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References No definition available. + Details
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- Definition Number of non-option equity instruments exercised by participants. + References No definition available. + Details
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- Definition Number of non-vested options outstanding. + References No definition available. + Details
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- Definition Number of non-vested options forfeited. + References No definition available. + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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