Income Taxes - Deferred tax assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Deferred tax assets attributable to:
Share-based compensation expense	$ 18,425	$ 17,082
Accrued liabilities	32,145	27,949
Inventory adjustments	4,492	3,055
Foreign loss carryforwards	36,419	35,315
Unrecognized tax benefits	532	471
Other	3,225	4,065
Total deferred tax assets	95,238	87,937
Valuation allowance	(36,571)	(34,965)
Total deferred tax assets, net	58,667	52,972
Deferred tax liabilities attributable to:
Depreciation and amortization	131,201	103,697
Total deferred tax liabilities	131,201	103,697
Net deferred tax liability	72,534	50,725
Domestic earnings before provision for income taxes	327,100	362,100	$ 361,800
Foreign earnings before provision for income taxes	27,000	16,400	$ 28,900
Accumulated undistributed earnings of the Company's foreign operations	263,000	233,200
Total operating loss carry-forward	117,900	114,200
Operating loss carry-forward, subject to valuation allowance	104,000	98,400
Amount of operating loss carry-forwards with an expiration date	13,900
Amount of operating loss carry-forwards without an expiration date	104,000
Total tax credit carryforwards	3,100	$ 3,400
Expiring tax credit carryforwards	1,900
Non-expiring tax credit carryforwards	$ 1,200