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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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 - The Amended Director Plan Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended						9 Months Ended
	Jun. 30, 2015	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016
Restricted stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, vested (in shares)		8,500	81,897	625,646	16,201	81,391	657,317
Number of shares granted (in shares)			54,310	286,256		112,397	434,283
Grant date fair value (in dollars per share)			$ 13.95	$ 13.85		$ 9.33	$ 8.44
Number of shares, forfeited (in shares)				167,712		7,500	588,819
Restricted stock \| Non-Management Director Compensation Plan (the Director Plan)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards vesting period								6 months
Restricted stock \| Non Management Directors Director Plan, Retainer Fee, June 12, 2015 through June 12, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted (in shares)	50,416
Grant date fair value (in dollars per share)	$ 13.17
Restricted stock \| Non Management Directors Director Plan, Triennial Service Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted (in shares)	90,000
Grant date fair value (in dollars per share)	$ 13.17
Restricted stock \| Non Management Directors Director Plan, Triennial Service Awards \| Tranche one
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted (in shares)								67,500
Restricted stock \| Non Management Directors Director Plan, Triennial Service Awards \| Vested in equal increments from June 2017 through June 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted (in shares)								22,500
Deferred Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation expense		$ 0.1			$ 0.1			$ 0.2	$ 0.3
Deferred Stock Units \| Non-Management Director Compensation Plan (the Director Plan)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-option shares, granted (in shares)								22,500
Number of shares, vested (in shares)		5,625	5,625	5,625	5,625	30,000
Number of shares, forfeited (in shares)						15,000
Deferred Stock Units \| Non-Management Director Compensation Plan (the Director Plan) \| Tranche one
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards vesting period								1 year
Number of shares, vested (in shares)								7,500
Deferred Stock Units \| Non-Management Director Compensation Plan (the Director Plan) \| Vested in equal increments from June 2017 through June 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards vesting period								2 years
Number of shares, vested (in shares)								15,000
Deferred Stock Units \| Prior Director Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-option shares, granted (in shares)								7,500
Deferred Stock Units \| Non Management Directors Director Plan, Triennial Service Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted (in shares)	90,000
Grant date fair value (in dollars per share)	$ 13.17
Deferred Stock Units \| Non Management Directors Director Plan, Triennial Service Awards \| Tranche one
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted (in shares)								58,125
Number of shares, forfeited (in shares)								15,000
Deferred Stock Units \| Non Management Directors Director Plan, Triennial Service Awards \| Vested in equal increments from June 2017 through June 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted (in shares)								16,875