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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic Net Income Per Share
Net income	$ 50,127	$ 24,503	$ 140,193	$ 61,877
Basic weighted average shares outstanding	44,961	44,141	44,754	44,018
Basic net income per share	$ 1.11	$ 0.56	$ 3.13	$ 1.41
Diluted Net Income Per Share
Net income	$ 50,127	$ 24,503	$ 140,193	$ 61,877
Basic weighted average shares outstanding	44,961	44,141	44,754	44,018
Effect of dilutive securities	1,192	1,557	1,410	1,637
Diluted weighted average shares outstanding	46,153	45,698	46,164	45,655
Diluted net income per share	$ 1.09	$ 0.54	$ 3.04	$ 1.36