Convertible Preferred Stock - Schedule of Conversion of Convertible Preferred Stock into Common Stock (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jul. 31, 2017	Jan. 31, 2017	Jan. 31, 2018
Temporary Equity [Line Items]
Number of shares authorized	10,679,599	10,651,216	100,000,000
Shares issued	10,610,966	10,610,966	0
Shares outstanding	10,610,966	10,610,966	0
Liquidation preference	$ 259,254	$ 259,254	$ 0
Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Date issued		2008-08
Number of shares authorized		1,533,329
Shares issued		1,533,329
Shares outstanding		1,533,329
Liquidation preference		$ 4,600
Series B Convertible Preferred Stock
Temporary Equity [Line Items]
Date issued		2009-07
Number of shares authorized		2,119,997
Shares issued		2,119,997
Shares outstanding		2,119,997
Liquidation preference		$ 12,000
Series C Convertible Preferred Stock
Temporary Equity [Line Items]
Date issued		2011-05
Number of shares authorized		1,312,311
Shares issued		1,312,311
Shares outstanding		1,312,311
Liquidation preference		$ 18,100
Series D Convertible Preferred Stock
Temporary Equity [Line Items]
Date issued		2012-07
Number of shares authorized		1,092,149
Shares issued		1,092,149
Shares outstanding		1,092,149
Liquidation preference		$ 25,000
Series E Convertible Preferred Stock
Temporary Equity [Line Items]
Date issued		2014-01
Number of shares authorized		1,681,912
Shares issued		1,641,662
Shares outstanding		1,641,662
Liquidation preference		$ 71,377
Series E-1 Convertible Preferred Stock
Temporary Equity [Line Items]
Date issued		2014-01
Number of shares authorized		83,333
Shares issued		83,333
Shares outstanding		83,333
Liquidation preference		$ 3,623
Series F Convertible Preferred Stock
Temporary Equity [Line Items]
Date issued	2017-02	2015-07
Number of shares authorized	28,383	2,828,185
Shares issued		2,828,185
Shares outstanding		2,828,185
Liquidation preference		$ 124,554