Goodwill and Intangible Assets - Finite Lived Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2019	Apr. 01, 2018	Sep. 30, 2018
Finite-lived intangible assets
Gross Amount	$ 87,347		$ 87,347		$ 86,237
Accumulated Amortization	(75,649)		(75,649)		(70,114)
Amortization expense	2,200	$ 5,000	6,200	$ 9,700
Estimated amortization expense
2019	3,691		3,691
2020	4,295		4,295
2021	2,256		2,256
2022	1,026		1,026
2023	430		430
Total	11,698		$ 11,698
Non-compete agreements
Finite-lived intangible assets
Weighted- Average Remaining Life (in Years)			0 years
Gross Amount	0		$ 0		83
Accumulated Amortization	0		$ 0		(83)
Client relations
Finite-lived intangible assets
Weighted- Average Remaining Life (in Years)			2 years 7 months 6 days
Gross Amount	54,277		$ 54,277		54,639
Accumulated Amortization	(48,733)		$ (48,733)		(46,449)
Backlog
Finite-lived intangible assets
Weighted- Average Remaining Life (in Years)			9 months 18 days
Gross Amount	25,042		$ 25,042		23,371
Accumulated Amortization	(22,552)		$ (22,552)		(20,007)
Trade names
Finite-lived intangible assets
Weighted- Average Remaining Life (in Years)			2 years 9 months 18 days
Gross Amount	8,028		$ 8,028		8,144
Accumulated Amortization	$ (4,364)		$ (4,364)		$ (3,575)