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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

X

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

+ Details

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- Definition

Number of non-option equity instruments forfeited.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans.

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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.

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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.

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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.

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No definition available.

+ Details

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- Definition

Number of non-option equity instruments exercised by participants.

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- Definition

Number of non-vested options outstanding.

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- Definition

Number of non-vested options forfeited.

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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.

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No definition available.

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