Revenue recognition - Rollforward of contract assets and contract liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019
Contract assets (unbilled accounts receivable)
Beginning balance	$ 636	$ 107
Contract asset additions	671	615
Amount transferred to receivables from contract assets	(631)	(86)
Ending balance	676	636
Contract liabilities (deferred revenue)
Beginning balance	6,488	4,886
Increases due to invoicing prior to satisfaction of performance obligations	11,650	5,900
Revenue recognized in the period	(7,485)
Performance obligations satisfied during the period that were included in the contract liability balance at the beginning of the period	(5,252)	(4,298)
Ending balance	$ 5,401	$ 6,488