Revenue (Schedule of Contract Liability) (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Sep. 30, 2018
Contract With Customer Liability [Line Items]
Current contract liabilities	[1]	$ 28,190	$ 9,659
Noncurrent contract liabilities	[2]	319,230	235,300
Deferred Revenue From Material Rights From GE Joint Venture Formation [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		6,988	7,087
Noncurrent contract liabilities		232,897	235,300
Deferred Revenue Advance Invoicing And/Or Prepayments From Customers [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		2,866	$ 2,572
Liability Related To Customer Supplied Inventory [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		17,283
Deferred Revenue From Material Rights Related To Engineering And Development Funding [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		1,053
Noncurrent contract liabilities		$ 86,333

[1] See Note 3, Revenue for more information on net current contract liabilities.

[2] See Note 3, Revenue, for more information on net noncurrent contract liabilities.