Revenue Recognition - Cash Flow Statement Impact of Adoption of ASC 606 (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2019	Apr. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income	$ 55,944	$ 28,747	$ 97,976	$ 74,799
Accounts receivable and contract assets			48,041	(42,912)
Contract liabilities			5,114	15,367
Income taxes receivable/payable			(3,951)	(1,213)
Net cash provided by operating activities			99,248	$ 23,593
Recognition Under Previous Guidance
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income			97,097
Accounts receivable and contract assets			32,716
Contract liabilities			21,598
Income taxes receivable/payable			(4,231)
Net cash provided by operating activities			99,248
Impact of the Adoption of ASC 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income			879
Accounts receivable and contract assets			15,325
Contract liabilities			(16,484)
Income taxes receivable/payable			280
Net cash provided by operating activities			$ 0