Number of aggregate shares issued in relation to share-based compensation arrangement.

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Grant date fair value of share-based awards other than options.

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Represents lower range of shares vested expressed as a percentage of target number of awards granted.

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Represents upper range of shares vested expressed as a percentage of target number of awards granted.

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Threshold, Percentage

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Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term for Expected Dividend Rate

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No definition available.

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Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term for Expected Volatility Rate

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Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term for Risk Free Interest Rate

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No definition available.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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).

+ References

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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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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Number of shares under non-option equity instrument agreements that were cancelled as a result of occurrence of a terminating event.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Percentage of vesting of share-based compensation awards.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of new stock issued during the period.

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Stock Based Compensation - Narrative (Details) - USD ($)	1 Months Ended		3 Months Ended
	May 31, 2017	May 31, 2015	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued, aggregate (in shares)					265,934
Performance Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		3 years
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested shares (in shares)			464,880	528,846	422,928	319,058
Shares granted (in shares)			206,597	326,663
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued, aggregate (in shares)			1,101,798		895,201
PSA Award \| Performance Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares that may be issued (in shares)			94,043
2017 Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares that may be issued (in shares)			5,570,000
Shares available for grant (in shares)			5,298,225
2017 Incentive Plan \| Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares)			58,920
2017 Incentive Plan \| Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares)			212,855
2017 Incentive Plan \| Performance Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares that may be issued (in shares)	588,535
Share-based compensation expense			$ 37,200
Unrecognized compensation cost			$ 2,300,000
Fair value of shares granted	$ 2,400,000
Award vesting period	3 years
2017 Incentive Plan \| Performance Share Awards \| Relative TSR performance Is Less Than The Thirtieth Percentile
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage	0.00%
2017 Incentive Plan \| Performance Share Awards \| Relative TSR Performance Is Equal To The Fiftieth Percentile
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage	100.00%
2017 Incentive Plan \| Performance Share Awards \| Board of Directors Chairman
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value, expected term	3 years
Fair value, expected term for volatility rate	3 years
2017 Incentive Plan \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested shares (in shares)			212,855
2010 Stock Incentive Plan \| Performance Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense			$ 31,300
Unrecognized compensation cost			10,400
2010 Stock Incentive Plan \| Performance Share Awards \| Board of Directors Chairman
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)		89,629
Fair value of shares granted		$ 400,000
Percentage of target PSA's granted eligible for receipt, minimum		0.00%
Percentage of target PSA's granted eligible for receipt, maximum		200.00%
Award vesting period	3 years	3 years
Award vesting threshold, percentage		0.33
Fair value, expected term		3 years
Fair value, expected term for volatility rate		3 years
Fair value, expected term for risk free interest rate		3 years
Fair value, expected term for dividend rate		3 years
2010 Stock Incentive Plan \| Performance Share Awards \| Board of Directors Chairman \| If TSR is Less Than 33%
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage		0.00%
2010 Stock Incentive Plan \| Performance Share Awards \| Board of Directors Chairman \| If TSR is Greater Than or Equal to 33%
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage		100.00%
2010 Stock Incentive Plan \| Performance Share Awards \| Board of Directors Chairman \| If TSR is Greater Than or Equal to 33% and TSR Is In Top Quartile of Identified Peer Group
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage		200.00%
2010 Stock Incentive Plan \| Performance Share Awards \| Board of Directors Chairman \| If TSR Is Greater Than or Equal to 33% and TSR Is In Bottom Quartile of Identified Peer Group
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage		50.00%
2010 Stock Incentive Plan \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense			$ 300,000
Forfeitures (in shares)			0	0
Unrecognized compensation cost			$ 2,400,000		$ 3,000,000
Unrecognized compensation cost, period for recognition			2 years 120 days
Fair value of vested shares			$ 900,000	$ 800,000
Requisite service period			3 years