Note 10 - Construction Joint Ventures (Details Textual) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Contract Value of Active Construction Joint Venture Projects	$ 3,400,000		$ 3,400,000
Contract with Customer, Liability, Total	195,267	$ 189,430	195,267	$ 189,430	$ 171,321
Revenue from Contract with Customer, Including Assessed Tax	1,062,129	1,065,189	2,696,214	2,616,887
Retained Earnings (Accumulated Deficit), Ending Balance	430,074	422,846	430,074	422,846	424,835
Net Income (Loss) Attributable to Parent, Total	$ 35,043	(91,162)	23,309	(153,127)
Unconsolidated Construction Joint Venture Net Income (Loss)			$ 8,027	(38,529)
Unconsolidated Construction Corporate Joint Venture [Member]
Number of Active Joint Venture Projects	10		10
Contract Value of Active Construction Joint Venture Projects	$ 11,600,000		$ 11,600,000
Contract with Customer, Liability, Total	225,800		225,800
Affirmative Claim Recovery Estimate	101,900	86,200	101,900	86,200	88,700
Back Charge Claims	14,100	13,800	14,100	13,800	13,100
Retained Earnings (Accumulated Deficit), Ending Balance	19,900	75,100	19,900	75,100	$ 82,500
Net Income (Loss) Attributable to Parent, Total	(9,300)	(6,000)	(11,500)	(144,500)
Unconsolidated Construction Joint Venture Net Income (Loss)	1,000	(8,000)	8,000	(38,500)
Unconsolidated Construction Corporate Joint Venture [Member] | Minimum [Member]
Contract Value of Active Construction Joint Venture Projects	13,700		13,700
Contract with Customer, Liability, Total	$ 1,200		$ 1,200
Equity Method Investment, Ownership Percentage	20.00%		20.00%
Unconsolidated Construction Corporate Joint Venture [Member] | Maximum [Member]
Contract Value of Active Construction Joint Venture Projects	$ 3,800,000		$ 3,800,000
Contract with Customer, Liability, Total	$ 52,800		$ 52,800
Equity Method Investment, Ownership Percentage	50.00%		50.00%
Unconsolidated Construction Corporate Joint Venture [Member] | Performance Guarantee [Member]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 300,000		$ 300,000
Guarantor Obligations, Current Carrying Value	82,300		82,300
Co-venturer [Member] | Performance Guarantee [Member]
Guarantor Obligations, Maximum Exposure, Undiscounted	500,000		500,000
Consolidated Construction Corporate Joint Venture [Member]
Contract Value of Active Construction Joint Venture Projects	$ 914,800		$ 914,800
Consolidated Construction Corporate Joint Venture [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Number of Active Joint Venture Projects	8		8
Contract Value of Active Construction Joint Venture Projects	$ 1,600,000		$ 1,600,000
Contract with Customer, Liability, Total	292,600		292,600
Revenue from Contract with Customer, Including Assessed Tax	117,400	79,200	314,900	219,900
Net Cash Provided by (Used in) Continuing Operations, Total			17,500	17,000
Consolidated Construction Corporate Joint Venture [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Minimum [Member]
Contract Value of Active Construction Joint Venture Projects	2,300		2,300
Contract with Customer, Liability, Total	800		$ 800
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage			50.00%
Consolidated Construction Corporate Joint Venture [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Maximum [Member]
Contract Value of Active Construction Joint Venture Projects	437,500		$ 437,500
Contract with Customer, Liability, Total	$ 97,300		$ 97,300
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage			70.00%
Line Item Joint Venture [Member]
Number of Active Joint Venture Projects	3		3
Contract Value of Active Construction Joint Venture Projects	$ 221,900		$ 221,900
Contract with Customer, Liability, Total	84,600		84,600
Revenue from Contract with Customer, Including Assessed Tax	$ 26,300	$ 27,500	55,000	$ 58,700
Unconsolidated Construction Joint Venture Net Income (Loss)			337,000
Construction [Member] | Unconsolidated Construction Corporate Joint Venture [Member]
Contract with Customer, Liability, Revenue Recognized			$ 800,000