Note 10 - Construction Joint Ventures (Details Textual) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Contract Value of Active Construction Joint Venture Projects	$ 3,400,000		$ 3,400,000
Contract with Customer, Liability, Total	174,850	$ 159,818	174,850	$ 159,818	$ 171,321
Revenue from Contract with Customer, Including Assessed Tax	964,172	915,771	1,634,085	1,551,698
Retained Earnings (Accumulated Deficit), Ending Balance	401,061	520,025	401,061	520,025	424,835
Net Income (Loss) Attributable to Parent, Total	$ 54,461	3,405	(11,734)	(61,965)
Unconsolidated Construction Joint Venture Net Income (Loss)			$ 6,972	(30,506)
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	297,000		297,000
Affirmative Claim Recovery Estimate	96,700	80,900	96,700	80,900	88,700
Back Charge Claims	14,100	18,000	14,100	18,000	13,100
Retained Earnings (Accumulated Deficit), Ending Balance	33,600	77,600	33,600	77,600	82,500
Net Income (Loss) Attributable to Parent, Total	13,800	27,500	(2,200)	(138,500)
Unconsolidated Construction Joint Venture Net Income (Loss)	6,600	(18,700)	7,000	(30,500)
Unconsolidated Construction Corporate Joint Venture [Member] | Minimum [Member]
Contract Value of Active Construction Joint Venture Projects	13,400		13,400
Contract with Customer, Liability, Total	$ 1,300		$ 1,300
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	$ 61,400		$ 61,400
Equity Method Investment, Ownership Percentage	50.00%		50.00%
Unconsolidated Construction Corporate Joint Venture [Member] | Performance Guarantee [Member]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 400		$ 400
Guarantor Obligations, Current Carrying Value	82,300	82,300	82,300	82,300	$ 82,300
Co-venturer [Member] | Performance Guarantee [Member]
Guarantor Obligations, Maximum Exposure, Undiscounted	600		600
Consolidated Construction Corporate Joint Venture [Member]
Contract Value of Active Construction Joint Venture Projects	$ 1,000,000		$ 1,000,000
Consolidated Construction Corporate Joint Venture [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Number of Active Joint Venture Projects	9		9
Contract Value of Active Construction Joint Venture Projects	$ 1,800,000		$ 1,800,000
Contract with Customer, Liability, Total	350,900		350,900
Revenue from Contract with Customer, Including Assessed Tax	114,900	86,000	197,500	140,700
Net Cash Provided by (Used in) Continuing Operations, Total			19,400	19,800
Consolidated Construction Corporate Joint Venture [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Minimum [Member]
Contract Value of Active Construction Joint Venture Projects	2,200		2,200
Contract with Customer, Liability, Total	1,000		$ 1,000
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	$ 115,800		$ 115,800
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	$ 172,200		$ 172,200
Line Item Joint Venture [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Contract with Customer, Liability, Total	61,200		61,200
Revenue from Contract with Customer, Including Assessed Tax	$ 20,100	$ 18,400	28,700	$ 31,200
Unconsolidated Construction Joint Venture Net Income (Loss)			280,200
Construction [Member] | Unconsolidated Construction Corporate Joint Venture [Member]
Contract with Customer, Liability, Revenue Recognized			$ 1,000