Basis of Presentation and Summary of Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017		Jul. 31, 2018	Jul. 31, 2017
Revenue:
Total revenue	$ 308,884	$ 224,670	[1]	$ 564,829	$ 407,315
As Previously Reported
Revenue:
Total revenue		224,461			407,092
Adjustment | Accounting Standards Update 2014-09
Revenue:
Total revenue		209			223
United States
Revenue:
Total revenue	229,760	165,620		414,678	312,125
United States | As Previously Reported
Revenue:
Total revenue		165,466			311,960
United States | Adjustment | Accounting Standards Update 2014-09
Revenue:
Total revenue		154			165
Rest of the world
Revenue:
Total revenue	$ 79,124	59,050		$ 150,151	95,190
Rest of the world | As Previously Reported
Revenue:
Total revenue		58,995			95,132
Rest of the world | Adjustment | Accounting Standards Update 2014-09
Revenue:
Total revenue		$ 55			$ 58

[1] * Prior period information has been adjusted to reflect the adoption impact of ASC 606, which we adopted on February 1, 2018.