Employee Benefit Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Postemployment Benefits [Abstract]
Employer matching contribution, percent of match	50.00%	50.00%	50.00%
Maximum annual contributions per employee, percent	6.00%	6.00%	6.00%
Employer contribution	$ 1.8	$ 0.9	$ 0.4
Defined Contribution Plan, Sponsor Location [Extensible List]	country:US	country:US	country:US
Defined Contribution Plan, Tax Status [Extensible List]	us-gaap:QualifiedPlanMember	us-gaap:QualifiedPlanMember	us-gaap:QualifiedPlanMember

Amount of discretionary contributions made by an employer to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Percentage employer matches of the employee's percentage contribution matched.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Indicates location of employer sponsoring defined contribution plan designed to provide retirement benefits.

No definition available.

Name:	us-gaap_DefinedContributionPlanSponsorLocationExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	srt-types:extensibleListItemType
Balance Type:	na
Period Type:	instant

Indicates tax status of defined contribution plan designed to provide retirement benefits.

No definition available.

Name:	us-gaap_DefinedContributionPlanTaxStatusExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	srt-types:extensibleListItemType
Balance Type:	na
Period Type:	instant

No definition available.

Name:	us-gaap_PostemploymentBenefitsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration