Note 4 - Accounts Receivable, Transit Accounts Receivable and Transit Accounts Payable (Details Textual) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Apr. 30, 2020	Sep. 26, 2020	Jun. 27, 2020	Dec. 28, 2019
Accounts Receivable, after Allowance for Credit Loss, Current, Total		$ 32,986		$ 59,760
Loss Contingency, Receivable, Ending Balance				14,100
Loss Contingency, Estimate of Possible Loss				10,300
Arbitration to Settle Dispute with Major Utility [Member]
Litigation Settlement, Amount Awarded from Other Party	$ 7,400
Litigation Settlement, Expense		8,400
Legal Fees		800
Accounts Receivable, Allowance for Credit Loss, Writeoff		700
Arbitration to Settle Dispute with Major Utility [Member] | Expense Related to Disputed Projects not Awards by Arbitrator [Member]
Litigation Settlement, Expense		6,700
Arbitration to Settle Dispute with Major Utility [Member] | Expense Related to Other Projects not Part of Arbitration [Member]
Litigation Settlement, Expense		700
Arbitration to Settle Dispute with Major Utility [Member] | Expense Related to Disputed Projects Part of Arbitration [Member]
Litigation Settlement, Expense		200
Collectibility of Receivables [Member]
Loss Contingency, Estimate of Possible Loss				10,300
Transit Accounts Receivable [Member]
Accounts Receivable, before Allowance for Credit Loss, Current			$ 200	4,900
Accounts Receivable, after Allowance for Credit Loss, Current, Total				300
Transit Accounts Payable [Member]
Accounts Payable, Current, Total			900	$ 4,600
Accounts Payable, Net			$ 700
Accounts Receivable not Part of Arbitration [Member]
Accounts Receivable, Allowance for Credit Loss, Writeoff		$ 700