Operations and summary of significant accounting policies (Schedule of reclassifications) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Operations And Summary Of Significant Accounting Policies [Line Items]
Amortization of Intangible Assets	$ 6,449	$ 6,439	$ 6,431	$ 6,458	$ 6,727	$ 6,887	$ 6,926	$ 6,946	$ 25,777	$ 27,486	$ 29,241
Cost of Sales [Member]
Operations And Summary Of Significant Accounting Policies [Line Items]
Prior Period Reclassification Adjustment	1,955	1,948	1,943	1,954	1,961	2,117	2,162	2,180	7,800	8,420	9,115
Selling, General and Administrative Expenses [Member]
Operations And Summary Of Significant Accounting Policies [Line Items]
Prior Period Reclassification Adjustment	$ 4,494	$ 4,491	$ 4,488	$ 4,504	$ 4,766	$ 4,770	$ 4,764	$ 4,766	$ 17,977	$ 19,066	$ 20,126