Long-Term Debt - Impact of Early Conversion, Convertible Notes Hedges and Warrants (Details) $ / shares in Units, $ in Thousands, shares in Millions	12 Months Ended
	Sep. 30, 2016 USD ($) $ / shares $ / share shares	Sep. 30, 2014 USD ($)
Debt Instrument [Line Items]
Net proceeds from sale of warrants		$ 25,106
Convertible Notes Hedges
Debt Instrument [Line Items]
Cost of hedge	$ 46,500
Cost of hedge, net of total proceeds from Warrants sold	$ 21,300
Common Class A | Convertible Notes Hedges
Debt Instrument [Line Items]
Notional amount (shares) | shares	14.3
Strike price (usd per share) | $ / share	16.065
Net-share-settled Warrants | Common Class A
Debt Instrument [Line Items]
Maximum shares called by warrant | shares	14.3
Strike price for warrants (usd per share) | $ / shares	$ 20.83
Net proceeds from sale of warrants	$ 25,100
Warrants outstanding | shares	14.3
2.125% Cash convertible senior notes due 2019 | If-Converted Scenario
Debt Instrument [Line Items]
Unamortized discount	$ 27,200
Unamortized debt issuance costs	$ 4,800