Stock-based Compensation - Classification of Stock-based Compensation (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018
Stock-based compensation:
Total stock-based compensation	$ 16,200	$ 15,130	$ 32,660	$ 29,325
Cost of revenue [Member]
Stock-based compensation:
Total stock-based compensation	320	317	587	632
Research and development [Member]
Stock-based compensation:
Total stock-based compensation	10,501	9,367	20,705	18,127
Selling, general and administrative [Member]
Stock-based compensation:
Total stock-based compensation	$ 5,379	$ 5,446	$ 11,368	$ 10,566