Equity Changes in stockholders' equity (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended		12 Months Ended
	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Oct. 31, 2019	Oct. 31, 2018	Jan. 31, 2019	Jan. 31, 2018	Feb. 01, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning of period	$ 225,139	$ 234,160	$ 84,549	$ 85,583	$ 88,565	$ 81,453	$ 84,549	$ 81,453	$ 81,453
Common stock offering, net of issuance costs of $530			146,470				$ 146,470
Exercise of stock options (in shares)							2,572,241
Exercise of stock options	3,406	4,137	4,996	4,942	5,232	4,910	$ 12,539		18,862
Vested restricted stock units converted to common shares	0	0	0	0	0	0	0		0
Issuance of restricted stock		0	0		0	0	0		0
Issuance of common stock under employee stock purchase plan	3,344		3,283	2,687		4,091	6,627		6,778
Stock-based compensation	21,601	17,025	13,472	13,218	11,081	8,066	52,098		44,907
Other comprehensive income	1,583	(892)	349	182	101	(95)	1,040		205
Net loss	(42,717)	(29,291)	(18,959)	(22,940)	(19,396)	(17,041)	(90,967)	(59,377)	(74,837)
Cumulative effect adjustment in connection with the adoption of ASU 2014-09											$ 7,181
End of period	$ 212,356	$ 225,139	$ 234,160	$ 83,672	$ 85,583	$ 88,565	212,356	$ 83,672	$ 84,549	$ 81,453
Issuance costs							$ 500
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning of period (in shares)	112,682,000	111,000,000	102,173,000	98,461,000	96,238,000	93,977,000	102,173,000	93,977,000	93,977,000
Beginning of period	$ 119	$ 117	$ 109	$ 105	$ 103	$ 100	$ 109	$ 100	$ 100
Common stock offering, net of issuance costs (in shares)			7,000,000				7,000,000
Common stock offering, net of issuance costs of $530			$ 7				$ 7
Exercise of stock options (in shares)	647,000	830,000	1,096,000	1,489,000	1,833,000	1,678,000	2,573,000		5,901,000
Exercise of stock options	$ 0	$ 1	$ 1	$ 1	$ 1	$ 2	$ 2		$ 5
Vested restricted stock units converted to common shares (in shares)	820,000	845,000	557,000	566,000	378,000	141,000	2,222,000		1,585,000
Vested restricted stock units converted to common shares	$ 1	$ 1		$ 1	$ 1		$ 2		$ 3
Issuance of restricted stock (in shares)		7,000	4,000		12,000	4,000	11,000		16,000
Issuance of common stock under employee stock purchase plans (in shares)	222,000		170,000	256,000		438,000	392,000		694,000
Issuance of common stock under employee stock purchase plan			$ 0			$ 1			$ 1
End of period (in shares)	114,371,000	112,682,000	111,000,000	100,772,000	98,461,000	96,238,000	114,371,000	100,772,000	102,173,000	93,977,000
End of period	$ 120	$ 119	$ 117	$ 107	$ 105	$ 103	$ 120	$ 107	$ 109	$ 100
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning of period	588,255	567,095	398,882	361,719	345,408	328,344	398,882	328,344	328,344
Common stock offering, net of issuance costs of $530			146,463				146,463
Exercise of stock options	3,406	4,136	4,995	4,941	5,231	4,908	12,537		18,857
Vested restricted stock units converted to common shares	(1)	(1)		(1)	(1)		(2)		(3)
Issuance of common stock under employee stock purchase plan	3,344		3,283	2,687		4,090	6,627		6,777
Stock-based compensation	21,601	17,025	13,472	13,218	11,081	8,066	52,098		44,907
End of period	616,605	588,255	567,095	382,564	361,719	345,408	616,605	382,564	398,882	328,344
Issuance costs			530							530
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning of period	(1,971)	(1,079)	(1,428)	(1,627)	(1,728)	(1,636)	(1,428)	(1,636)	(1,636)
Other comprehensive income	1,583	(892)	349	182	101	(95)	1,040		205
Cumulative effect adjustment in connection with the adoption of ASU 2014-09											3
End of period	(388)	(1,971)	(1,079)	(1,445)	(1,627)	(1,728)	(388)	(1,445)	(1,428)	(1,636)
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning of period	(349,359)	(320,068)	(301,109)	(262,709)	(243,313)	(233,450)	(301,109)	(233,450)	(233,450)
Net loss	(42,717)	(29,291)	(18,959)	(22,940)	(19,396)	(17,041)	(90,967)		(74,837)
Cumulative effect adjustment in connection with the adoption of ASU 2014-09											$ 7,178
End of period	(392,076)	(349,359)	(320,068)	(285,649)	(262,709)	(243,313)	(392,076)	(285,649)	(301,109)	(233,450)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning of period	(11,905)	(11,905)	(11,905)	(11,905)	(11,905)	(11,905)	(11,905)	(11,905)	(11,905)
End of period	$ (11,905)	$ (11,905)	$ (11,905)	$ (11,905)	$ (11,905)	$ (11,905)	$ (11,905)	$ (11,905)	$ (11,905)	$ (11,905)