Supplemental financial statement information (Investments) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018	Jan. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Marketable equity securities, at fair value	$ 81,130		$ 81,130		$ 0
Non-marketable equity securities	500		500		500
Equity method investments	209		209		209
Total equity investments	81,839		81,839		$ 709
Unrealized gain on marketable equity securities	$ 3,774	$ 0	$ 27,285	$ 0