Summary of Unrecognized Stock-Based Compensation Expense, Net of Estimated Forfeitures (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Time-based stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Expense, Net of Estimated Forfeitures	$ 124,295
Weighted-average Recognition Period	2 years 7 months 6 days
Performance-based stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Expense, Net of Estimated Forfeitures	$ 59,416
Performance-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Expense, Net of Estimated Forfeitures	14,649
ESPP share issuances
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Expense, Net of Estimated Forfeitures	$ 970
Weighted-average Recognition Period	3 months 29 days

Unrecognized cost of unvested share-based compensation awards.

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

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

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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