Fair Value Measurements - Summary of Changes in the Fair Value of Company's Level 3 Financial Liabilities (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Liability for Class A Redeemable Common Shares [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 10,632
Exercise of stock options	432
Change in fair value	19,223
Modification to stock options as a result of the Company's IPO	(30,287)
Liability for Stock-Based Compensation Awards [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	11,604
Exercise of stock options	(411)
Forfeitures of stock options	(157)
Change in fair value	25,191
Modification to stock options as a result of the Company's IPO	$ (36,227)

Fair value measurement with unobservable inputs reconciliations recurring basis liability exercise of stock options.

No definition available.

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- Definition

Fair value measurement with unobservable inputs reconciliations recurring basis liability forfeiture of stock options.

+ References

No definition available.

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- Definition

Fair value measurement with unobservable inputs reconciliations recurring basis modification to stock options.

+ References

No definition available.

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- Definition

Amount of unrealized (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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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.

+ References

No definition available.

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- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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