Computation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Basic Net Income Per Share
Net income	$ 36,847	$ 13,446	$ 24,503	$ 37,374	$ 14,899	$ 15,432	$ 8,875	$ 12,910	$ 112,170	$ 52,116	$ 38,147
Weighted average shares used in computing basic net income per share									44,153	43,238	42,204
Net income per share - basic	$ 0.83	$ 0.30	$ 0.56	$ 0.85	$ 0.34	$ 0.36	$ 0.21	$ 0.30	$ 2.54	$ 1.21	$ 0.90
Diluted Net Income Per Share
Net income	$ 36,847	$ 13,446	$ 24,503	$ 37,374	$ 14,899	$ 15,432	$ 8,875	$ 12,910	$ 112,170	$ 52,116	$ 38,147
Weighted average shares used in computing basic net income per share									44,153	43,238	42,204
Effect of dilutive securities									1,696	1,420	2,691
Weighted average shares used in computing diluted net income per share									45,849	44,658	44,895
Net income per share - diluted	$ 0.80	$ 0.29	$ 0.54	$ 0.82	$ 0.33	$ 0.34	$ 0.20	$ 0.29	$ 2.45	$ 1.17	$ 0.85