Stock-Based Compensation - 2017 Market-Based RSAs and RSUs (Details) - 2017 Market-Based RSAs and RSUs - TSR and Performance Measures - Senior Management - USD ($) $ in Millions		3 Months Ended
Jan. 17, 2017	Mar. 31, 2018
Market-Based RSAs and RSUs
Stock-based compensation
Timeframe for calculation of TSR	2 years
Minimum payout of shares (in shares)	0
Maximum payout of shares (in shares)	406,868
Aggregate value recognized as compensation expense	$ 3.2
Market-Based RSAs and RSUs \| Vesting on February 20, 2019
Stock-based compensation
Vesting percentage	66.70%
Market-Based RSAs and RSUs \| Vesting on February 20, 2020
Stock-based compensation
Vesting percentage	33.30%
Market-Based RSAs
Stock-based compensation
Granted (in shares)	353,508
Forfeited (in shares)		233,448
Reversal of previously recognized compensation expense		$ 0.8
Market-Based RSUs
Stock-based compensation
Granted (in shares)	53,360

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Represents the minimum payout of shares granted upon the actual performance against the Performance Measures.

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No definition available.

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Represents information pertaining to period over which the relative total shareholder return is to be calculated to enable vesting of share-based payment awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of cost (reversal of cost) for employee benefits and share-based payment arrangement. Includes, but is not limited to, pension, other postretirement, postemployment and termination benefits.

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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=96867065&loc=d3e5070-113901

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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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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Percentage of vesting of share-based compensation awards.

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-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Value, before forfeitures, of stock or other type of equity granted of any equity-based compensation plan other than an employee stock ownership plan (ESOP).

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