Fair Value Measurements (Rollforward of Earn-outs) (Details) - USD ($) $ in Thousands		9 Months Ended
		Jun. 30, 2020	Oct. 01, 2019	Sep. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Option and purchase right		$ 506		$ 0
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Earn-outs related to acquisitions, beginning balance		1,545
Payments		(187)
Fair value adjustment		(1,267)
Earn-outs related to acquisitions, ending balance		91
Option and purchase right		7,167
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Other Current Liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Earn-outs related to acquisitions, beginning balance	[1]	611
Payments		(187)
Fair value adjustment	[1]	(333)
Earn-outs related to acquisitions, ending balance	[1]	91
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Other Noncurrent Liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Earn-outs related to acquisitions, beginning balance	[2]	934
Payments		0
Fair value adjustment	[2]	(934)
Earn-outs related to acquisitions, ending balance	[2]	0
Frontier [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Remaining percentage to be acquired			40.00%
Frontier [Member] | Other Current Liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Option and purchase right		506
Frontier [Member] | Other Noncurrent Liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Option and purchase right		$ 6,661

[1] Included in Accrued expenses and other liabilities on the Consolidated Balance Sheets.

[2] Included in Other non‑current liabilities on the Consolidated Balance Sheets.