Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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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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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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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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Stock-Based Compensation - Service Based Restricted Stock Units (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Weighted Average Grant Date Fair Value
Stock based compensation expenses	$ 1,501,326	$ 1,365,332	$ 3,018,628	$ 1,811,335
Restricted stock units - Service based awards
Number of Shares
Outstanding at beginning of period (in shares)			472,959
Granted (in shares)		0		0
Outstanding at end of period (in shares)	669,247		669,247
Weighted Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share)			$ 4.32
Granted (in dollars per share)			4.45
Forfeited (in dollars per share)			4.81
Unvested, Weighted Average Grant-Date Fair Value	$ 4.36		$ 4.32
Stock based compensation expenses	$ 400,000	$ 0	$ 800,000	$ 0
Granted (in shares)		0		0
Unrecognized stock-based compensation expenses	$ 1,800,000
Minimum \| Restricted stock units - Service based awards
Weighted Average Grant Date Fair Value
Vesting period			1 year
Maximum \| Restricted stock units - Service based awards
Weighted Average Grant Date Fair Value
Vesting period			3 years