Note 2 - Accounting Policies (Details Textual) $ in Thousands		12 Months Ended
	Oct. 01, 2019 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares		Dec. 31, 2017 USD ($) shares
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax, Total		$ 10,900
Foreign Currency Transaction Gain (Loss), Realized		(503)	$ (623)		$ (2,152)
Research and Development Expense, Total		$ 6,400	5,600		4,200
Retainage Collection Period Upon Completion of Contract		1 year
Percentage of Retainage Balance, Retainage Receivables Aged Greater than 365 Days		18.00%
Impairment of Intangible Assets, Finite-lived		$ 0	2,169		41,032
Number of Reporting Units	6
Reporting Unit, Fair Value in Below of Carrying Amount, Number of Reporting Units	0
Reporting Unit, Percentage of Fair Value in Below of Carrying Amount	10.00%
Goodwill, Ending Balance		256,835	260,633		260,715
Goodwill, Impairment Loss		$ 0	$ 1,389	[1]	45,390
Fyfe [Member]
Goodwill, Ending Balance					9,600
Goodwill, Impairment Loss					45,400
Energy Services [Member]
Goodwill, Ending Balance	$ 48,000
Trademarks [Member] | Fyfe [Member]
Impairment of Intangible Assets, Finite-lived					3,400
Customer Relationships [Member] | Fyfe [Member]
Impairment of Intangible Assets, Finite-lived					20,800
Patents and Acquired Technology [Member] | Fyfe [Member]
Impairment of Intangible Assets, Finite-lived					$ 16,800
Minimum [Member]
Construction Period		1 month
Collection Period for Municipalities		60 days
Retainage, Percent of Contract Value Withheld		5.00%
Collection Period for Other than Municipalities		30 days
Minimum [Member] | Measurement Input, Discount Rate [Member]
Goodwill, Measurement Input	0.120
Minimum [Member] | Measurement Input, Long-term Revenue Growth Rate [Member]
Goodwill, Measurement Input	0.016
Maximum [Member]
Construction Period		24 months
Collection Period for Municipalities		90 days
Retainage, Percent of Contract Value Withheld		15.00%
Collection Period for Other than Municipalities		45 days
Maximum [Member] | Measurement Input, Discount Rate [Member]
Goodwill, Measurement Input	0.160
Maximum [Member] | Measurement Input, Long-term Revenue Growth Rate [Member]
Goodwill, Measurement Input	0.049
Stock Options and Restricted and Deferred Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | shares		529,539			735,577
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | shares			4,049		73,897
Other Expense [Member]
Foreign Currency Transaction Gain (Loss), Realized		$ 500	$ (600)		$ (2,200)

[1] During 2018, the Company recorded goodwill of $2.7 million and $1.3 million related to the acquisitions of Hebna and P2S, respectively (see Note 1).