Revenue, Deferred Revenue and Remaining Performance Obligations - Deferred contract acquisition costs (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jan. 31, 2019	Jul. 31, 2018	Jan. 31, 2017
Deferred contract acquisition costs
Balance, beginning	$ 64,197		$ 21,764		$ 63,071
Capitalization of contract acquisition costs	19,317	$ 19,300	9,272	$ 27,788	14,298
Amortization of deferred contract acquisition costs	(7,731)		(6,395)	(15,076)	(11,991)
Balance, ending	75,783	64,197	24,641	75,783	24,641
Deferred contract acquisition costs, current						$ 34,017	$ 28,847	$ 18,808
Deferred contract acquisition costs, noncurrent						41,766	$ 9,918	5,833
Total deferred contract acquisition costs	$ 64,197	$ 64,197	$ 21,764	$ 75,783	$ 63,071	$ 75,783		$ 24,641	$ 22,334