Stock-based Compensation - RSU Activity (Details) - 2015 Omnibus Incentive Plan - Restricted Stock Units (RSUs) - $ / shares	6 Months Ended	9 Months Ended	12 Months Ended
Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Units
Beginning period, outstanding (in shares)		307,000	416,000
Units vested (in shares)	(2,000)	(89,000)	(93,000)
Units forfeited (in shares)		(15,000)	(14,000)
Units granted (in shares)		70,000		111,281	390,352
Ending period, outstanding (in shares)	307,000	273,000	309,000	416,000
Weighted Average Grant-Date Fair Value
Beginning period, outstanding (in dollars per share)		$ 9.84	$ 9.87
Units vested (in dollars per share)	$ 9.56	10.02	9.97
Units forfeited (in dollars per share)		8.81	9.95
Units granted (in dollars per share)		5.76
Ending period, outstanding (in dollars per share)	$ 9.84	$ 8.79	$ 9.84	$ 9.87

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

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.

+ References

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-Publisher FASB
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- Definition

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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-Name Accounting Standards Codification
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-Paragraph 2
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- Definition

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).

+ References

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-Publisher FASB
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-Paragraph 2
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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

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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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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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Publisher FASB
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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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No definition available.

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