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 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) - $ / shares	1 Months Ended		3 Months Ended						9 Months Ended
	Jun. 30, 2015	Jan. 31, 2015	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2016
Restricted stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, vested (in shares)			16,201	81,391	657,317	28,461	63,017	644,247
Number of shares, granted (in shares)				112,397	434,283		140,416	441,256
Grant date fair value (in dollars per share)				$ 9.33	$ 8.44		$ 13.17	$ 16.21
Number of shares, forfeited (in shares)				7,500	588,819	26,125		43,660
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, First Half of 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, granted (in shares)		18,200
Grant date fair value (in dollars per share)		$ 16.10
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)	37,500
Restricted stock \| Non Management Directors Director Plan, Triennial Service Awards \| Tranche Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, granted (in shares)	52,500
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
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) \| Tranche Two
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)									35,625
Number of shares, forfeited (in shares)	15,000
Deferred Stock Units \| Non Management Directors Director Plan, Triennial Service Awards \| Tranche Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, granted (in shares)	39,375