Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015
Financial assets that are measured at fair value on a recurring basis
Holding Period Adjustment		$ 4	$ 132
Phantom Share-based Awards		(3,932)
Contingent consideration	$ (2,575)	(2,601)	(2,914)
Net financial assets (liabilities)	5,119	7,640	5,781
Foreign currency forwards
Financial assets that are measured at fair value on a recurring basis
Derivative assets	7,694	14,169	8,563
Cash Convertible Notes Hedges
Financial assets that are measured at fair value on a recurring basis
Derivative assets	3,219	10,505	27,215
Cash Convertible Notes Embedded Derivative
Financial assets that are measured at fair value on a recurring basis
Derivative liability	(3,219)	(10,505)	(27,215)
Level 1
Financial assets that are measured at fair value on a recurring basis
Holding Period Adjustment		0	0
Phantom Share-based Awards		0
Contingent consideration	0	0	0
Net financial assets (liabilities)	0	0	0
Level 1 | Foreign currency forwards
Financial assets that are measured at fair value on a recurring basis
Derivative assets	0	0	0
Level 1 | Cash Convertible Notes Hedges
Financial assets that are measured at fair value on a recurring basis
Derivative assets	0	0	0
Level 1 | Cash Convertible Notes Embedded Derivative
Financial assets that are measured at fair value on a recurring basis
Derivative liability	0	0	0
Level 2
Financial assets that are measured at fair value on a recurring basis
Holding Period Adjustment		4	132
Phantom Share-based Awards		0
Contingent consideration	0	0	0
Net financial assets (liabilities)	7,694	14,173	8,695
Level 2 | Foreign currency forwards
Financial assets that are measured at fair value on a recurring basis
Derivative assets	7,694	14,169	8,563
Level 2 | Cash Convertible Notes Hedges
Financial assets that are measured at fair value on a recurring basis
Derivative assets	3,219	10,505	27,215
Level 2 | Cash Convertible Notes Embedded Derivative
Financial assets that are measured at fair value on a recurring basis
Derivative liability	(3,219)	(10,505)	(27,215)
Level 3
Financial assets that are measured at fair value on a recurring basis
Holding Period Adjustment		0	0
Phantom Share-based Awards		(3,932)
Contingent consideration	(2,575)	(2,601)	(2,914)
Net financial assets (liabilities)	(2,575)	(6,533)	(2,914)
Level 3 | Foreign currency forwards
Financial assets that are measured at fair value on a recurring basis
Derivative assets	0	0	0
Level 3 | Cash Convertible Notes Hedges
Financial assets that are measured at fair value on a recurring basis
Derivative assets	0	0	0
Level 3 | Cash Convertible Notes Embedded Derivative
Financial assets that are measured at fair value on a recurring basis
Derivative liability	$ 0	$ 0	$ 0