Reportable Segments - Revenue by Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 28, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	$ 132,598	$ 131,032	$ 127,974	$ 117,335	$ 115,344	$ 104,185	$ 104,018	$ 94,534	$ 508,938	$ 418,081	$ 333,034
INF
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues									331,161	254,723
BTS
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues									177,777	163,358
Public and quasi-public sector
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues									338,479	278,788
Public and quasi-public sector | INF
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues									271,935	233,395
Public and quasi-public sector | BTS
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues									66,544	45,393
Private sector
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues									170,459	139,293
Private sector | INF
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues									59,226	21,328
Private sector | BTS
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues									$ 111,233	$ 117,965