Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2017	Sep. 30, 2016
Prepaid expenses and other current assets | Not Designated as Hedging Instrument | Level 3 | Foreign Currency Forwards
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guarantee asset	$ 562	$ 1,209
Accounts payable, accrued expenses and other current liabilities | Not Designated as Hedging Instrument | Level 3 | Foreign Currency Forwards
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guarantee liability	(584)	(1,258)
Other assets, net | Level 2 | Cash Convertible Notes Hedges — Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	15,138	37,692
Long-term debt, net | Level 2 | Cash Convertible Notes Embedded Derivative — Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	$ (15,138)	$ (37,692)