Accrued Liabilities (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019
Accrued Liabilities Current [Abstract]
Salaries and other member benefits	$ 43,803		$ 50,850
Warranties	18,576	$ 21,079	18,972	$ 21,770	$ 18,927	$ 27,309
Interest payable	14,547		15,281
Accrued retirement benefits	3,013		3,051
Restructuring charges	403		3,395
Taxes, other than income	25,027		13,925
Net current contract liabilities	28,760		24,620
Other	30,221		21,700
Accrued liabilities	$ 164,350		$ 151,794