Income Taxes - Federal Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Rate reconciliation
Tax at federal statutory rate									$ 48,800	$ 52,000	$ 52,400
State income tax, net of federal benefit									8,400	7,000	(1,300)
Foreign residual income									39,500	35,800	9,900
Nondeductible costs									15,800	7,600	2,500
Return to provision									3,200	(3,100)	(700)
Foreign tax rate differential									(3,400)	(5,300)	(5,000)
Income tax credits and incentives									(47,800)	(44,700)	(28,600)
Valuation allowance									(15,900)	(26,500)	37,800
Change in uncertain tax positions									5,100	(200)	(21,200)
Exclusion of tax on non-controlling interests									(8,300)	5,600	(26,000)
Tax exempt income										(4,600)	(27,700)
Audit settlement									5,100	3,900	7,400
Impact of changes in tax law										1,500	(12,500)
Other items, net									5,500	(4,700)	(700)
Income tax expense (benefit) for continuing operations	$ 15,300	$ (7,200)	$ 21,700	$ 15,900	$ 16,600	$ 27,200	$ 12,200	$ (42,500)	$ 45,753	$ 13,498	$ (3,494)
Major elements contributing to the difference between the U.S. federal statutory rate of 21% for fiscal year 2020 and 24.5% for fiscal years ended 2019 and 2018 and the effective tax rate
Federal statutory rate (as a percent)									21.00%	21.00%	24.50%	35.00%
State income tax, net of federal benefit (as a percent)									3.60%	2.80%	(0.60%)
Foreign residual income (as a percent)									17.00%	14.50%
Foreign residual income (as a percent)											(4.60%)
Nondeductible costs (as a percent)									6.80%	3.10%	1.20%
Change in uncertain tax positions (as a percent)									2.20%	(0.10%)	(9.90%)
Return to provision, primarily foreign tax credits (as a percent)									1.40%	(1.30%)	(0.30%)
Income tax credits and incentive (as a percent)									(20.60%)	(18.10%)	(13.40%)
Valuation allowance (as a percent)									(6.90%)	(10.70%)	17.70%
Exclusion of tax on non-controlling interests (as a percent)									(3.60%)	2.30%	(12.20%)
Foreign tax rate differential (as a percent)									(1.50%)	(2.10%)	(2.30%)
Audit settlement (as a percent)									(2.20%)	(1.60%)	(3.50%)
Tax exempt income (as a percent)										(1.90%)	(13.00%)
Change in tax rates (as a percent)										(0.60%)	5.90%
Other items, net (as a percent)									2.50%	(1.90%)	(0.40%)
Total income tax expense (as a percent)									19.70%	5.40%	(1.70%)