Revenue - Unearned Revenue (Details) $ in Thousands	6 Months Ended
	Mar. 31, 2019 USD ($)
Unearned Revenue [Roll Forward]
Unearned revenue, beginning of period	$ 3,933	[1]
Billings	13,613
Revenue recognized	(10,497)
Unearned revenue, end of period	$ 7,049

[1] Prior period information has been restated for the adoption of ASU No. 2014-09, “Revenue from Contracts with Customers (Topic 606),” which we adopted on October 1, 2018.