Computation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Basic Net Income Per Share
Net income	$ 44,862	$ 13,446	$ 185,056	$ 75,323
Basic weighted average shares outstanding	45,046	44,247	44,852	44,095
Basic net income per share	$ 1.00	$ 0.30	$ 4.13	$ 1.71
Diluted Net Income Per Share
Net income	$ 44,862	$ 13,446	$ 185,056	$ 75,323
Basic weighted average shares outstanding	45,046	44,247	44,852	44,095
Effect of dilutive securities	1,090	1,622	1,295	1,636
Diluted weighted average shares outstanding	46,136	45,869	46,147	45,731
Diluted net income per share	$ 0.97	$ 0.29	$ 4.01	$ 1.65