Sale of Building (Details) $ in Thousands			3 Months Ended			12 Months Ended
		Oct. 02, 2018 USD ($) ft²	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)		Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)		Sep. 30, 2017 USD ($)	[1]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale				$ 5,220	[1]	$ 0	$ 5,220	[1]
Gain on sale						4,392	622	[1]	$ (25)
Minnetonka, MN
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate sold (in sqft) | ft²		130,000
Proceeds from sale of building		$ 10,000
Assets held for sale	[1]			5,200			$ 5,200
Tax benefit related to sale of building				$ 1,100
Gain on sale			$ 4,400
Gain on sale, net of deferred tax			$ 3,400
Leasehold Improvements | Hopkins, MN
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments for leasehold improvements						$ 5,800
Useful life						10 years

[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.