Employee Benefits and Stock-based Compensation - Classification of Stock-based Compensation (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Stock-based compensation:
Total stock-based compensation	$ 15,692	$ 8,535	$ 4,999
Cost of revenue [Member]
Stock-based compensation:
Total stock-based compensation	343	178	92
Research and development [Member]
Stock-based compensation:
Total stock-based compensation	8,654	4,887	2,942
Selling, general and administrative [Member]
Stock-based compensation:
Total stock-based compensation	$ 6,695	$ 3,470	$ 1,965