Computation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic Net Income Per Share
Net income	$ 62,213	$ 44,588	$ 13,071	$ 88,923	$ 106,801	$ 101,994
Weighted average shares – basic	45,104		45,319		45,057	45,267
Net income per share – basic	$ 1.38		$ 0.29		$ 2.37	$ 2.25
Diluted Net Income Per Share
Net income	$ 62,213	$ 44,588	$ 13,071	$ 88,923	$ 106,801	$ 101,994
Weighted average shares – basic	45,104		45,319		45,057	45,267
Effect of dilutive securities	557		593		552	764
Weighted average shares – diluted	45,661		45,912		45,609	46,031
Net income per share – diluted	$ 1.36		$ 0.28		$ 2.34	$ 2.22