Stock Options - Additional Information (Detail) - USD ($)	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of unissued common stock available for grant under the plans (in shares)	3,100,000
Granted (in shares)	0
Share-based compensation expense	$ 8,600,000	$ 7,700,000
Proceeds from exercise of stock options	$ 0	0
Performance-Based Units \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares which will vest after achievement of goals (in shares)	0
Performance-Based Units \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares which will vest after achievement of goals (in shares)	2.0
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 7,800,000	6,100,000
Total unrecognized compensation cost	$ 12,400,000
Unrecognized compensation cost, Weighted-average recognition period	2 years 1 month 6 days
Aggregate weighted-average grant-date fair value of units granted	$ 14,300,000	12,600,000
Aggregate weighted-average grant-date fair value of units vested	7,300,000	3,500,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	800,000	1,600,000
Total intrinsic value of options exercised	0	$ 0
Total unrecognized compensation cost	$ 400,000
Unrecognized compensation cost, Weighted-average recognition period	1 year

Share Based Compensation Arrangement By Share Based Payment Award Number of Shares Vesting After Achievement of Goals

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- Definition

Share-based compensation arrangement by share-based payment award, other than options, grants in period, weighted average grant date fair value.

+ References

No definition available.

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- Definition

Share-based compensation arrangement by share-based payment award, other than options, vested in period, weighted average grant date fair value.

+ References

No definition available.

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

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- Definition

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.

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- Definition

Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

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-Publisher FASB
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- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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- Definition

Net number of share options (or share units) granted during the period.

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