Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		5 Months Ended	6 Months Ended		7 Months Ended	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Dec. 31, 2017	Jan. 31, 2018	Jan. 31, 2017	Jul. 31, 2018	Jul. 31, 2018	Jul. 31, 2017
Income Taxes [Line Items]
U.S. Federal statutory tax rate	27.00%	35.00%	35.00%	27.00%	35.00%
Discrete tax benefit	$ 7,000,000			$ 7,000,000
Provisional estimate amount for one-time transition tax	6,500,000			6,500,000
Tax expense for net shortfall on exercise of stock compensation	500,000			500,000
Provisional amount of tax expense on remeasurement of deferred tax balance	3,000,000			$ 3,000,000
Provisional estimate amount for one-time transition tax, payment period				8 years
Unrecognized tax benefits, accrued interest and penalties	200,000			$ 200,000				$ 100,000
Unrecognized tax benefits, for uncertain tax positions	$ 4,500,000			$ 4,500,000
Maximum
Income Taxes [Line Items]
Discrete tax benefit		$ 400,000			$ 400,000
Scenario Forecast
Income Taxes [Line Items]
U.S. Federal statutory tax rate						21.00%	27.00%