Income Taxes - Unrecognized Tax Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Income Taxes [Abstract]
Unrecognized Tax Benefits Beginning Balance	$ 51,968	$ 55,867
Unrecognized Tax Benefits, Increases Resulting from Current Period Tax Positions	13	207
Unrecognized Tax Benefits, Increases Resulting from Prior Period Tax Positions	272	0
Unrecognized Tax Benefits, Reductions Resulting from Lapse of Applicable Statute of Limitations	3,361	3,707
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	0	399
Unrecognized Tax Benefits, Decreases Resulting from Settlements with Taxing Authorities	0	0
Unrecognized Tax Benefits, Reductions Resulting from Rate Change	18,636	0
Unrecognized Tax Benefits Ending Balance	$ 30,256	$ 51,968