Fair Value Measurements - Narrative (Details) $ in Thousands, £ in Millions	6 Months Ended
	Mar. 29, 2019 GBP (£)	Mar. 29, 2019 USD ($)	Sep. 30, 2018 GBP (£)	Sep. 30, 2018 USD ($)
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward currency contracts | £	£ 45.8		£ 49.1
Measurement Input, Expected Term | Minimum | Foreign Exchange Contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit Derivative, Term	6 months
Measurement Input, Expected Term | Maximum | Foreign Exchange Contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit Derivative, Term	6 years
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward currency contracts | $		$ 0		$ 0