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, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
Revenue from External Customer [Line Items]
Total revenue	$ 62,474	$ 71,630	$ 119,412	$ 135,765
Taiwan [Member]
Revenue from External Customer [Line Items]
Total revenue	39,144	48,052	72,350	94,468
Asia Pacific [Member]
Revenue from External Customer [Line Items]
Total revenue	18,045	12,291	34,401	24,050
Europe [Member]
Revenue from External Customer [Line Items]
Total revenue	2,875	6,444	7,457	8,344
North America other than United States [Member]
Revenue from External Customer [Line Items]
Total revenue	1,503	2,979	3,509	4,984
United States [Member]
Revenue from External Customer [Line Items]
Total revenue	$ 907	$ 1,864	$ 1,695	$ 3,919