Income Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Sep. 30, 2015
Income Tax Contingency [Line Items]
Effective income tax rate	17.00%	8.00%	15.00%	10.00%
Gains on extinguishment of debt	$ 50,466	$ 0	$ 58,863	$ 0
Deferred income tax benefit	22,900
Deferred income tax benefit, valuation allowance	22,900
US statutory rate			35.00%
Unrecognized tax benefits	15,400		$ 15,400
Windfall tax benefits from stock option exercises					$ 19,800
Windfall tax benefits from share-based payment arrangements			14,797	$ 0
Other long-term liabilities
Income Tax Contingency [Line Items]
Estimated accrued interest and penalties	4,100		$ 4,100
6.5% Senior Notes | Senior Notes
Income Tax Contingency [Line Items]
Gains on extinguishment of debt	$ 58,863