Differences Between Statutory and Effective Income Tax Rate (Detail)	1 Months Ended	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Statutory income tax rate	35.00%	21.00%	31.50%	21.00%	31.50%
Excess tax benefits from stock-based awards		(2.60%)	(7.00%)	(41.50%)	(21.90%)
Credits		(1.70%)	(2.10%)	(1.70%)	(2.10%)
State taxes, net		4.30%	3.70%	4.30%	3.70%
Permanent differences		1.80%	1.70%	1.80%	1.70%
Effect of the Tax Reform Act on net deferred tax assets			42.10%		19.60%
Excess foreign tax credits		7.90%		3.70%
Other		(0.20%)	0.70%	0.10%	0.20%
Effective tax rate		30.50%	70.60%	(12.30%)	32.70%