Income Taxes - Components of income (loss) and provision for income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Components of income (loss) before income taxes
United States	$ (55,634)	$ (57,176)	$ (18,712)
Foreign	59,484	49,699	90,623
Income (loss) before income taxes	3,850	(7,477)	71,911
Current:
Federal	(4,330)	2,469	(2,433)
State	816	(231)	723
Foreign	13,869	8,249	20,266
Total current	10,355	10,487	18,556
Deferred:
Federal	2,839	(15,614)	24,112
State	710	(4,365)	5,710
Foreign	1,155	280	619
Total deferred	4,704	(19,699)	30,441
Provision for income taxes	$ 15,059	$ (9,212)	$ 48,997