Operations and summary of significant accounting policies (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended			24 Months Ended	36 Months Ended
	Sep. 30, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2016	Sep. 30, 2016
Depreciation expense		$ 41,550	$ 45,994	$ 43,773
Selling, general, and administrative expenses include net foreign currency transaction gains (losses)		701	$ (1,721)	(1,089)
Goodwill, Impairment Loss						$ 0
Asset Impairment Charges	$ 3,138			$ 3,138	$ 0
Service Life [Member]
Depreciation expense		$ (12,000)