Stock-based Compensation - Additional Information (Detail) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock options	$ 107.6
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, remaining weighted-average period for recognition	3 years 1 month 6 days
Restricted Common Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, remaining weighted-average period for recognition	1 year 7 months 6 days
Total unrecognized compensation expense	$ 9.4

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

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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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