Segment Reporting - Company's Revenue by Geographic Region Based on Bill-to Location (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Revenue from External Customer [Line Items]
Total revenue	$ 71,630	$ 65,142	$ 135,765	$ 122,299
Taiwan [Member]
Revenue from External Customer [Line Items]
Total revenue	48,052	46,803	94,468	88,905
Asia Pacific [Member]
Revenue from External Customer [Line Items]
Total revenue	12,291	11,577	24,050	19,163
Europe [Member]
Revenue from External Customer [Line Items]
Total revenue	6,444	3,282	8,344	8,634
North America other than United States [Member]
Revenue from External Customer [Line Items]
Total revenue	2,979	1,095	4,984	1,365
United States [Member]
Revenue from External Customer [Line Items]
Total revenue	$ 1,864	$ 2,385	$ 3,919	$ 4,232