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

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

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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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Net number of non-option equity instruments granted to participants.

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Equity-Based Compensation - Non-Management Director Equity-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Jun. 30, 2015	Jan. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense			$ 0.4	$ 0.3	$ 0.2
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, vested (in shares)			2,816,884	766,159	785,820
Number of shares, granted (in shares)			340,566	555,680	581,672
Weighted average fair value, granted (in dollars per share)			$ 13.87	$ 8.37	$ 15.48
Number of shares forfeited in period (in shares)			167,712	626,319	70,299
Non-Management - Amended Directors Director Plan \| Deferred stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted in period (in shares)			22,500
Number of shares, vested (in shares)			33,750	41,250	22,500
Number of shares, granted (in shares)					90,000
Weighted average fair value, granted (in dollars per share)					$ 13.17
Number of shares forfeited in period (in shares)				15,000
Non-Management - Amended Directors Director Plan \| Deferred stock units \| First anniversary of grant date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			1 year
Number of shares, vested (in shares)			7,500
Non-Management - Amended Directors Director Plan \| Deferred stock units \| Tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			2 years
Number of shares, vested (in shares)			15,000
Non-Management - Amended Directors Director Plan \| Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			6 months
Prior Director Plan \| Deferred stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted in period (in shares)			7,500
Non-Management Directors Director Plan, retainer fee, first half of 2015 \| Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, granted (in shares)		18,200
Weighted average fair value, granted (in dollars per share)		$ 16.10
Non-Management Directors Director Plan, retainer fee, June 12, 2015 through June 12, 2016 \| Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, granted (in shares)	50,416
Weighted average fair value, granted (in dollars per share)	$ 13.17
Non-Management Directors Director Plan, triennial service awards \| Deferred stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, granted (in shares)	90,000
Weighted average fair value, granted (in dollars per share)	$ 13.17
Non-Management Directors Director Plan, triennial service awards \| Deferred stock units \| Tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares forfeited in period (in shares)			15,000
Non-Management Directors Director Plan, triennial service awards \| Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, granted (in shares)	90,000
Weighted average fair value, granted (in dollars per share)	$ 13.17