Long-Term Debt - Cash Convertible Senior Notes (Details) - 2.125% Cash Convertible Senior Notes Due 2019 - USD ($)	1 Months Ended		12 Months Ended
	Jul. 31, 2014	Jun. 30, 2014	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Jul. 31, 2017
Debt Instrument [Line Items]
Convertible senior notes issued and settled	$ 30,000,000	$ 200,000,000
Stated interest rate		2.125%	2.125%			2.875%
Interest expense			$ 15,500,000	$ 15,500,000	$ 14,100,000
Contractual interest expense			4,700,000	4,900,000	4,900,000
Debt discount amortization			$ 10,800,000	$ 10,600,000	$ 9,200,000
Interest rate at period end			8.00%
Remaining unamortized issuance discount period			2 years