Fair Value Measurement (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration related to acquisitions	$ 4,643		$ 8,400
Payment of contingent consideration	3,800	$ 3,100
Business Combination, Consideration Transferred, Liabilities Incurred	3,200	2,700
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration related to acquisitions	4,643	16,594	$ 8,400	$ 19,570
Payment of contingent consideration		$ 3,050
Level 3 | Accrued Expenses and Other Current Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration related to acquisitions	$ 4,600