Business Acquisitions - Narrative (Details)																	12 Months Ended
	Nov. 08, 2019 USD ($)	Jul. 02, 2019 USD ($)	Jul. 01, 2019 USD ($) installments shares	Jun. 03, 2019 USD ($) installments shares	Mar. 22, 2019 USD ($) installments	Dec. 31, 2018 USD ($) installments shares	Nov. 02, 2018 USD ($) installments shares	Aug. 24, 2018 USD ($) installments shares	Feb. 02, 2018 USD ($) installments shares	Jan. 12, 2018 USD ($) installments shares	Dec. 22, 2017 USD ($) shares	Sep. 06, 2017 USD ($) installments shares	Jun. 06, 2017 USD ($) installments shares	May 04, 2017 USD ($) installments shares	May 01, 2017 USD ($) installments shares	Apr. 14, 2017 USD ($)	Dec. 28, 2019 USD ($)	Dec. 29, 2018 USD ($)	Dec. 30, 2017 USD ($)	Dec. 20, 2019 USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses																	$ 1,202,000	$ 728,000	$ 563,000
Excess working capital																	8,781,000
Cash paid at closing																	6,677,000
Other commitment																	358,187,000	46,986,000		$ 150,000,000
Revolving commitments																				$ 215,000,000.0
Total consideration																	369,954,000	93,628,000
Earn-out of cash fair value																	4,002,000	4,698,000	1,890,000
Promissory note incurred																	1,004,000	3,112,000
Working capital adjustment reduction of purchase price																			2,360,000
Business combination, acquisition related costs																	1,492,000	1,267,000	$ 1,398,000
Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Other commitment																	36,217,000	40,001,000
AR Credit agreement
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses																	318,000,000
Revolving commitments																	215,000,000
WHPacific, Inc.
Acquired Finite-Lived Intangible Assets [Line Items]
Total consideration		$ 9,000,000
GHD Services, Inc
Acquired Finite-Lived Intangible Assets [Line Items]
Total consideration	$ 8,300,000
GeoDesign, Inc
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses			$ 8,500,000
Total consideration			12,800,000
Consideration transferred of common stock			$ 375,000
Common stock number of shares | shares			4,731
Common stock purchase price			$ 425,000
Earn-out of cash			1,500,000
Earn-out of cash fair value			198,000
GeoDesign, Inc | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable			$ 2,000,000														2,000,000
Promissory note interest rate			4.00%
Number of installments | installments			4
Periodic payment			$ 500,000
Alta Environmental, L.P
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses				$ 4,000,000
Total consideration				6,500,000
Earn-out of cash				500,000
Earn-out of cash fair value				323,000
Alta Environmental, L.P | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable				$ 2,000,000
Promissory note interest rate				4.00%
Number of installments | installments				4
Periodic payment				$ 500,000
Page One consultants
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses				2,000,000
Total consideration				3,900,000
Consideration transferred of common stock				$ 200,000
Common stock number of shares | shares				2,647
Common stock purchase price				$ 200,000
Earn-out of cash				500,000
Earn-out of cash fair value				$ 448,000
Page One consultants | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable																	1,000,000
Promissory note interest rate				3.00%
Number of installments | installments				3
Promissory note incurred				$ 1,000,000
Periodic payment				$ 333,000
Acquisition of The Sextant Group
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses					$ 7,000,000
Total consideration					$ 11,000,000
Acquisition of The Sextant Group | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable																	3,140,000
Promissory note interest rate					4.00%
Number of installments | installments					4
Promissory note incurred					$ 4,000,000
Periodic payment					$ 1,000,000
Celtic Energy, Inc
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses						$ 1,000,000
Total consideration						1,900,000
Consideration transferred of common stock						$ 200,000
Common stock number of shares | shares						3,227
Common stock purchase price						$ 200,000
Earn-out of cash						200,000
Earn-out of cash fair value						$ 181,000
Celtic Energy, Inc | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable																	300,000
Promissory note interest rate						3.00%
Number of installments | installments						3
Promissory note incurred						$ 300,000
Periodic payment						$ 100,000
CHI Engineering Inc.
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses							$ 30,000,000
Consideration transferred of common stock							$ 3,000,000
Common stock number of shares | shares							36,729
Common stock purchase price							$ 3,000,000
Earn-out of cash							2,000,000
Earn-out of cash fair value							1,547,000
Periodic payment							$ 1,000,000
Liability interest rate							3.00%
CHI Engineering Inc. | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable																	11,250,000	15,000,000
Promissory note interest rate							3.00%
Number of installments | installments							4
Number of equal installments | installments							3
Promissory note incurred							$ 15,000,000
Periodic payment							3,750,000
CHI Engineering Inc. | Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Total consideration							$ 53,000,000
CALYX Engineers and Consultants Inc.
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses								$ 25,000,000
Total consideration								34,000,000
Consideration transferred of common stock								$ 3,000,000
Common stock number of shares | shares								36,379
CALYX Engineers and Consultants Inc. | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable																	3,000,000	4,000,000
Promissory note interest rate								3.75%
Number of installments | installments								4
Promissory note incurred								$ 4,000,000
Periodic payment								1,000,000
CALYX Engineers and Consultants Inc. | Cash Payable Within 120 Days
Acquired Finite-Lived Intangible Assets [Line Items]
Promissory note incurred								$ 2,000,000
CSA (M&E) Ltd.
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses									$ 2,000,000
Total consideration									4,200,000
Consideration transferred of common stock									$ 150,000
Number of equal installments | installments									2
Common stock number of shares | shares									2,993
Common stock purchase price									$ 250,000
Earn-out of cash									1,200,000
Earn-out of cash fair value									899,000
Periodic payment									125,000
Business combination, consideration transferred, liabilities incurred including earn-out amount									$ 1,200,000
CSA (M&E) Ltd. | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable																	450,000	600,000
Promissory note interest rate									3.00%
Number of installments | installments									4
Promissory note incurred									$ 600,000						$ 2,200,000
Periodic payment									$ 150,000
Butsko Utility Design, Inc.
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses										$ 1,500,000
Total consideration										4,250,000
Consideration transferred of common stock										$ 300,000
Number of equal installments | installments										2
Common stock number of shares | shares										5,630
Common stock purchase price										$ 600,000
Earn-out of cash										850,000
Earn-out of cash fair value										666,000
Periodic payment										$ 300,000
Butsko Utility Design, Inc. | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable																	750,000	1,000,000
Promissory note interest rate										3.00%
Number of installments | installments										4
Promissory note incurred										$ 1,000,000
Periodic payment										$ 250,000
Skyscene LLC
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses											$ 250,000
Total consideration											650,000
Consideration transferred of common stock											$ 400,000
Common stock number of shares | shares											7,434
Marron and Associates, Inc.
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses												$ 400,000
Consideration transferred of common stock												$ 67,000
Common stock number of shares | shares												1,510
Common stock purchase price												$ 133,000
Business combination, consideration transferred, cash and equity interest issued and issuable												133,000
Marron and Associates, Inc. | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Earn-out of cash fair value												$ 90,000
Marron and Associates, Inc. | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable																	100,000	200,000
Promissory note interest rate												3.00%
Number of installments | installments												3
Promissory note incurred												$ 300,000
Periodic payment												100,000
Marron and Associates, Inc. | Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Total consideration												$ 990,000
Richard D. Kimball Co., Inc.
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses													$ 15,000,000
Consideration transferred of common stock													$ 667,000
Common stock number of shares | shares													18,072
Common stock purchase price													$ 1,333,000
Business combination, consideration transferred, cash and equity interest issued and issuable													$ 1,333,000
Richard D. Kimball Co., Inc. | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable																	2,750,000	4,125,000
Promissory note interest rate													3.00%
Number of installments | installments													4
Promissory note incurred													$ 5,500,000
Periodic payment													1,375,000
Richard D. Kimball Co., Inc. | Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Total consideration													$ 22,500,000
Holdrege & Kull, Consulting Engineers and Geologists
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses														$ 1,000,000
Consideration transferred of common stock														$ 100,000
Common stock number of shares | shares														2,628
Earn-out of cash														$ 500,000
Earn-out of cash fair value														405,000
Periodic payment														125,000
Business combination, consideration transferred, liabilities incurred including earn-out amount														$ 500,000
Holdrege & Kull, Consulting Engineers and Geologists | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable																	300,000	450,000
Promissory note interest rate														3.00%
Number of installments | installments														4
Promissory note incurred														$ 600,000
Periodic payment														150,000
Holdrege & Kull, Consulting Engineers and Geologists | Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Total consideration														$ 2,200,000
Lochrane Engineering, Inc.
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to acquire businesses															2,690,000
Consideration transferred of common stock															$ 17,000
Common stock number of shares | shares															441
Earn-out of cash															$ 550,000
Business combination, consideration transferred, cash and equity interest issued and issuable															$ 33,000
Lochrane Engineering, Inc. | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Number of installments | installments															4
Lochrane Engineering, Inc. | Uncollateralized promissory notes
Acquired Finite-Lived Intangible Assets [Line Items]
Notes Payable																	825,000	$ 1,238,000
Promissory note interest rate															3.00%
Number of installments | installments															4
Earn-out of cash fair value															$ 413,000
Promissory note incurred															1,650,000
Business combination, consideration transferred, liabilities incurred including earn-out amount															2,200,000
Debt instrument, periodic payment including earnt-out amount, total															550,000
Lochrane Engineering, Inc. | Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Total consideration															$ 4,940,000
Bock & Clark Corporation
Acquired Finite-Lived Intangible Assets [Line Items]
Total consideration																$ 42,000,000
NV5 and QSI
Acquired Finite-Lived Intangible Assets [Line Items]
Business combination, acquisition related costs																	$ 19,099,000