Computation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Basic Net Income Per Share
Net income	$ 88,923	$ 90,066
Weighted average shares - basic	45,215	44,546
Net income per share - basic	$ 1.97	$ 2.02
Diluted Net Income Per Share
Net income	$ 88,923	$ 90,066
Weighted average shares - basic	45,215	44,546
Effect of dilutive securities	877	1,623
Weighted average shares - diluted	46,092	46,169
Net income per share - diluted	$ 1.93	$ 1.95