Employee Benefit Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Compensation Related Costs [Abstract]
Pay contributed by employer	50.00%
Pay contributed by employee	6.00%
Contribution to 401 (K) Plan	$ 2.6	$ 1.5	$ 1.5

Amount of contribution received by defined benefit plan from employer which increases plan assets.

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