Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interest
Beginning Balance at Sep. 30, 2016	$ 594,205	$ 541	$ 318,723	$ 319,808	$ (44,089)	$ (778)
Beginning balance (shares) at Sep. 30, 2016		54,099
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation	1,808		1,808
Release of restricted stock	2	$ 2
Release of restricted stock (shares)		178
Taxes paid related to net share settlement of equity awards	(706)		(706)
Foreign currency translation adjustment	(3,465)				(3,488)	23
Net income (loss)	7,038			7,165		(127)
Ending Balance at Dec. 31, 2016	598,882	$ 543	319,825	326,973	(47,577)	(882)
Ending balance (shares) at Dec. 31, 2016		54,277
Beginning Balance at Sep. 30, 2017	659,926	$ 544	348,532	351,666	(38,367)	(2,449)
Beginning balance (shares) at Sep. 30, 2017		54,398
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation	2,889		2,889
Release of restricted stock	1	$ 1
Release of restricted stock (shares)		66
Taxes paid related to net share settlement of equity awards	(311)		(311)
Foreign currency translation adjustment	(6,575)				(6,535)	(40)
Net income (loss)	12,133			12,748		(615)
Ending Balance at Dec. 31, 2017	$ 668,063	$ 545	$ 351,110	$ 364,414	$ (44,902)	$ (3,104)
Ending balance (shares) at Dec. 31, 2017		54,464