Stock-Based Compensation Plans - Summary of Unrecognized Stock-based Compensation Expense (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized expense	$ 8.4
Weighted Average Remaining Vesting Period (Years)	1 year 6 months
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized expense	$ 3.0
Weighted Average Remaining Vesting Period (Years)	1 year 3 months 19 days
Restricted Stock Units (RSU)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized expense	$ 2.0
Weighted Average Remaining Vesting Period (Years)	1 year 3 months 19 days
Performance Share Units (PSU)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized expense	$ 3.4
Weighted Average Remaining Vesting Period (Years)	1 year 8 months 12 days

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.

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

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- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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