Trade Accounts Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Sep. 30, 2015
Current trade accounts receivable
Trade accounts receivable	$ 10,830				$ 17,841	$ 15,209
Allowance for doubtful accounts	(1,395)				(2,449)	(2,516)
Total current trade accounts receivable	$ 9,435	$ 8,327	$ 16,709	$ 13,819	$ 15,392	$ 12,693