Summary of Significant Accounting Policies - Difference Between Federal Statutory Rate and Effective Tax Rate (Detail)	1 Months Ended	2 Months Ended	3 Months Ended	7 Months Ended	9 Months Ended	12 Months Ended
Aug. 13, 2018	Sep. 30, 2018	Sep. 30, 2019	Aug. 13, 2018	Sep. 30, 2019	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Tax at statutory rate	21.00%	21.00%	21.00%	21.00%	21.00%	35.00%
Tax effect of:
State income taxes, net of federal benefit	4.50%	2.00%	(1.80%)	3.90%
Valuation allowance on deferred tax assets	(21.10%)	(0.60%)	4.50%	(24.10%)	2.30%
Transaction costs			8.60%		1.90%
Nondeductible stock-based compensation	(0.70%)	(0.20%)	1.20%	(0.70%)	1.50%
Other	(7.40%)		2.70%	(1.30%)
Effective tax rate	(3.70%)	22.20%	36.20%	(1.20%)	26.70%

Effective income tax rate reconciliation transaction costs.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to nondeductible expense for share-based payment arrangement.

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