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, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018
Basic Net Income Per Share
Net income	$ 69,217	$ 13,071	$ 88,923	$ 44,862	$ 50,127	$ 90,066	$ 171,211	$ 185,056
Weighted average shares - basic	45,140			45,046			45,225	44,852
Net income per share - basic	$ 1.53			$ 1.00			$ 3.79	$ 4.13
Diluted Net Income Per Share
Net income	$ 69,217	$ 13,071	$ 88,923	$ 44,862	$ 50,127	$ 90,066	$ 171,211	$ 185,056
Weighted average shares - basic	45,140			45,046			45,225	44,852
Effect of dilutive securities	555			1,090			710	1,295
Weighted average shares - diluted	45,695			46,136			45,935	46,147
Net income per share - diluted	$ 1.51			$ 0.97			$ 3.73	$ 4.01