Computation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Basic Net Income Per Share
Net income	$ 90,066	$ 37,374
Weighted average shares used in computing basic net income per share	44,546	43,895
Net income per share - basic	$ 2.02	$ 0.85
Diluted Net Income Per Share
Net income	$ 90,066	$ 37,374
Weighted average shares used in computing basic net income per share	44,546	43,895
Effect of dilutive securities	1,623	1,713
Weighted average shares used in computing diluted net income per share	46,169	45,608
Net income per share - diluted	$ 1.95	$ 0.82