Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2017	Sep. 30, 2016	Jun. 30, 2016
Convertible Hedges and Embedded Derivative Financial Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Expected volatility rate	44.00%	55.00%	53.00%
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	$ 298	$ 1,209	$ 0
Accounts payable, accrued expenses and other current liabilities | Level 3 | Cash Convertible Notes Warrants — Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	(523)	0	0
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	(310)	(1,258)	0
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	5,900	37,692	16,200
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	$ (5,900)	$ (37,692)	$ (16,200)
Minimum | Cash Convertible Notes Warrants — Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Expected volatility rate	32.00%
Maximum | Cash Convertible Notes Warrants — Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Expected volatility rate	34.00%