Differences Between Statutory Income Tax Rate and Effective Income Tax Rate (Detail)		3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Statutory income tax rate (blended)		31.50%		31.50%
Statutory income tax rate	35.00%		35.00%		35.00%
Excess tax benefits from stock-based awards		(7.00%)		(21.90%)
Credits		(2.10%)	(1.20%)	(2.10%)	(1.20%)
State taxes, net		3.70%	3.30%	3.70%	3.30%
Permanent differences		1.70%	2.70%	1.70%	2.70%
Effect of the Tax Reform Act on net deferred tax assets		42.10%		19.60%
Other		0.70%	0.40%	0.20%	0.20%
Effective tax rate		70.60%	40.20%	32.70%	40.00%