Note 4 - Accounts Receivable, Transit Accounts Receivable and Transit Accounts Payable (Details Textual) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Apr. 30, 2020	Mar. 28, 2020	Dec. 28, 2019
Accounts Receivable, after Allowance for Credit Loss, Current, Total		$ 50,767	$ 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, Expense		8,000
Legal Fees		400
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
Arbitration to Settle Dispute with Major Utility [Member] | Subsequent Event [Member]
Litigation Settlement, Amount Awarded from Other Party	$ 7,400
Collectibility of Receivables [Member]
Loss Contingency, Estimate of Possible Loss			10,300
Transit Accounts Receivable [Member]
Accounts Receivable, before Allowance for Credit Loss, Current		1,900	4,900
Accounts Payable, Current, Total		2,500
Accounts Payable, Net		600
Accounts Receivable, after Allowance for Credit Loss, Current, Total			300
Transit Accounts Payable [Member]
Accounts Payable, Current, Total			$ 4,600
Accounts Receivable not Part of Arbitration [Member]
Accounts Receivable, Allowance for Credit Loss, Writeoff		$ 700