Revenue - Unearned Revenue (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2018 USD ($)
Contract With Customer, Liability [Roll Forward]
Unearned revenue, beginning of period	$ 3,933	[1]
Billings	9,702
Revenue recognized	(5,326)
Unearned revenue, end of period	$ 8,309

[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.