Note 2 - Accounting Policies (Details)	3 Months Ended		12 Months Ended			24 Months Ended		12 Months Ended					12 Months Ended		12 Months Ended				12 Months Ended
	Jun. 30, 2013 USD ($)	Jun. 30, 2013 EUR (€)	Dec. 31, 2013 USD ($) segment	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2015 GBP (£)	Dec. 31, 2013 Minimum [Member]	Dec. 31, 2013 Maximum [Member]	Jun. 30, 2013 Insituform-Germany [Member]	Dec. 31, 2013 WCU [Member]	Dec. 31, 2013 Bayou Coating [Member]	Dec. 31, 2013 Bayou [Member] USD ($)	Oct. 02, 2013 Bayou [Member]	Dec. 31, 2013 Fyfe NA [Member]	Oct. 02, 2013 Fyfe NA [Member]	Oct. 02, 2013 Bayou and Fyfe NA [Member] USD ($)	Dec. 31, 2013 Delta Double Jointing [Member]	Dec. 31, 2013 Goodwill [Member] reportingUnit
Note 2 - Accounting Policies [Line Items]
Number of Reportable Segments			4																9
Retainage, Percent of Contract Value Withheld								5.00%	15.00%
Research and Development Expense			$ 2,600,000	$ 1,800,000	$ 2,200,000
Fair Value Inputs, Discount Rate								13.00%	16.50%				13.50%		16.00%
Compound Annual Growth Rate Assumption								2.00%	17.00%				10.00%		17.00%
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax			600,000	14,300,000
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax			1,200,000	800,000
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax			200,000	200,000
Noncontrolling Interest, Ownership Percentage by Parent	50.00%	50.00%								50.00%								59.00%
Business Combination, Consideration Transferred	18,300,000	14,000,000
Gain (Loss) on Disposition of Business	11,300,000
Business Acquisition, Transaction Costs	500,000
Long-term Purchase Commitment, Amount (in Pounds)						3,600,000	2,300,000
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners											49.00%							41.00%
Equity Method Investment, Ownership Percentage												49.00%
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures			9,101,000	19,181,000
Fair Value Inputs, Long-term Revenue Growth Rate								1.00%	3.50%				3.00%		3.50%
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount														2.80%		5.40%
Reporting Unit, Change in Fair Value, Value													32,300,000
Reporting Unit, Change in Fair Value, Percent													17.20%		2.70%
Goodwill			$ 334,180,000	$ 272,294,000													$ 72,900,000
Contract Receivable Retainage, Due after Next Twelve Months			12.00%