Goodwill and Intangible Assets - Finite Lived Assets (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Jun. 26, 2016	Mar. 27, 2016	Jun. 28, 2015	Jun. 26, 2016	Jun. 28, 2015	Sep. 27, 2015
Finite-lived intangible assets
Gross Amount	$ 141,419			$ 141,419		$ 112,116
Accumulated Amortization	(89,428)			(89,428)		(71,784)
Foreign currency translation adjustments				1,000
Amortization expense for identifiable intangible assets	6,300		$ 4,700	16,100	$ 15,500
Estimated amortization expense
2016	6,368			6,368
2017	22,595			22,595
2018	11,864			11,864
2019	5,450			5,450
2020	4,279			4,279
Beyond	1,435			1,435
Total	51,991			$ 51,991
RME | Coffey and INDUS
Finite-lived intangible assets
Identifiable intangible assets added on acquisition		$ 21,000
WEI | Coffey and INDUS
Finite-lived intangible assets
Identifiable intangible assets added on acquisition		$ 5,700
Non-compete agreements
Finite-lived intangible assets
Weighted-Average Remaining Life				7 months 6 days
Gross Amount	874			$ 874		819
Accumulated Amortization	(779)			$ (779)		(587)
Client relations
Finite-lived intangible assets
Weighted-Average Remaining Life				3 years 4 months 24 days
Gross Amount	119,377			$ 119,377		106,676
Accumulated Amortization	(80,729)			$ (80,729)		(67,726)
Backlog
Finite-lived intangible assets
Weighted-Average Remaining Life				1 year 8 months 12 days
Gross Amount	18,607			$ 18,607		2,115
Accumulated Amortization	(5,589)			$ (5,589)		(1,444)
Technology and trade names
Finite-lived intangible assets
Weighted-Average Remaining Life				1 year
Gross Amount	2,561			$ 2,561		2,506
Accumulated Amortization	$ (2,331)			$ (2,331)		$ (2,027)