Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Financial assets that are measured at fair value on a recurring basis
Holding Period Adjustment		$ 4
Phantom Share-based Awards	$ (2,099)	(3,932)
Contingent consideration	(2,601)	(2,601)	$ (3,440)
Net financial assets (liabilities)	4,799	7,640	6,547
Foreign currency forwards
Financial assets that are measured at fair value on a recurring basis
Derivative assets	9,499	14,169	9,987
Cash Convertible Notes Hedges
Financial assets that are measured at fair value on a recurring basis
Derivative assets	7,777	10,505	45,163
Cash Convertible Notes Embedded Derivative
Financial assets that are measured at fair value on a recurring basis
Derivative liability	(7,777)	(10,505)	(45,163)
Level 1
Financial assets that are measured at fair value on a recurring basis
Holding Period Adjustment		0
Phantom Share-based Awards	0	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
Phantom Share-based Awards	0	0
Contingent consideration	0	0	0
Net financial assets (liabilities)	9,499	14,173	9,987
Level 2 | Foreign currency forwards
Financial assets that are measured at fair value on a recurring basis
Derivative assets	9,499	14,169	9,987
Level 2 | Cash Convertible Notes Hedges
Financial assets that are measured at fair value on a recurring basis
Derivative assets	7,777	10,505	45,163
Level 2 | Cash Convertible Notes Embedded Derivative
Financial assets that are measured at fair value on a recurring basis
Derivative liability	(7,777)	(10,505)	(45,163)
Level 3
Financial assets that are measured at fair value on a recurring basis
Holding Period Adjustment		0
Phantom Share-based Awards	(2,099)	(3,932)
Contingent consideration	(2,601)	(2,601)	(3,440)
Net financial assets (liabilities)	(4,700)	(6,533)	(3,440)
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