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, 2019	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic Net Income Per Share
Net income	$ 13,071	$ 88,923	$ 50,127	$ 90,066	$ 101,994	$ 140,193
Weighted average shares - basic	45,319		44,961		45,267	44,754
Net income per share - basic	$ 0.29		$ 1.11		$ 2.25	$ 3.13
Diluted Net Income Per Share
Net income	$ 13,071	$ 88,923	$ 50,127	$ 90,066	$ 101,994	$ 140,193
Weighted average shares - basic	45,319		44,961		45,267	44,754
Effect of dilutive securities	593		1,192		764	1,410
Weighted average shares - diluted	45,912		46,153		46,031	46,164
Net income per share - diluted	$ 0.28		$ 1.09		$ 2.22	$ 3.04