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, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018
Revenue from External Customer [Line Items]
Total revenue	$ 56,410	$ 62,474	$ 103,598	$ 119,412
Taiwan [Member]
Revenue from External Customer [Line Items]
Total revenue	30,981	39,144	58,581	72,350
Asia Pacific [Member]
Revenue from External Customer [Line Items]
Total revenue	17,246	18,045	31,734	34,401
Europe [Member]
Revenue from External Customer [Line Items]
Total revenue	4,101	2,875	7,584	7,457
North America other than United States [Member]
Revenue from External Customer [Line Items]
Total revenue	3,001	1,503	3,884	3,509
United States [Member]
Revenue from External Customer [Line Items]
Total revenue	$ 1,081	$ 907	$ 1,815	$ 1,695