Income Taxes - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended		6 Months Ended
	Dec. 22, 2017	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
U.S. federal statutory corporate tax rate		35.00%	21.00%	35.00%	21.00%	35.00%
Income tax provision (benefit)			$ 1,706,000	$ 7,981,000	$ (39,873,000)	$ 4,399,000
Effective income tax rate			3.30%	24.60%	(39.70%)	6.60%
Measurement period	1 year
Income tax expense			$ 0		$ 0
Excess tax benefits from stock-based awards			$ 12,900,000	$ 4,500,000	$ 66,800,000	$ 21,300,000
Potential repatriation of foreign subsidiary earnings					100.00%