Note 9 - Construction Joint Ventures (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Contract with Customer, Liability, Total	$ 171,321	$ 95,737	$ 109,011
Contract Value of Active Construction Joint Venture Projects	3,400,000
Revenue from Contract with Customer, Including Assessed Tax	3,562,459	3,445,606	3,287,031
Retained Earnings (Accumulated Deficit), Ending Balance	424,835	594,353
Net Income (Loss) Attributable to Parent, Total	(145,117)	(60,191)	582
Unconsolidated Construction Joint Venture Net Income (Loss)	(51,486)	(120,632)	(44,689)
Unconsolidated Construction Corporate Joint Venture [Member]
Contract with Customer, Liability, Total	$ 452,700
Number of Active Joint Venture Projects	10
Contract Value of Active Construction Joint Venture Projects	$ 11,600,000
Affirmative Claim Recovery Estimate	88,700	116,800
Back Charge Claims	13,100	15,900
Retained Earnings (Accumulated Deficit), Ending Balance	82,500	76,200
Net Income (Loss) Attributable to Parent, Total	274,400	422,500	240,300
Unconsolidated Construction Joint Venture Net Income (Loss)	51,500	120,600	44,600
Unconsolidated Construction Corporate Joint Venture [Member] | Minimum [Member]
Contract with Customer, Liability, Total	1,100
Contract Value of Active Construction Joint Venture Projects	$ 13,200
Equity Method Investment, Ownership Percentage	20.00%
Unconsolidated Construction Corporate Joint Venture [Member] | Maximum [Member]
Contract with Customer, Liability, Total	$ 106,800
Contract Value of Active Construction Joint Venture Projects	$ 3,800,000
Equity Method Investment, Ownership Percentage	50.00%
Unconsolidated Construction Corporate Joint Venture [Member] | Performance Guarantee [Member]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 600,000
Guarantor Obligations, Current Carrying Value	82,300	81,900
Unconsolidated Construction Corporate Joint Venture [Member] | Construction [Member]
Contract with Customer, Liability, Total	1,500,000
Co-venturer [Member] | Performance Guarantee [Member]
Guarantor Obligations, Maximum Exposure, Undiscounted	900,000
Consolidated Construction Corporate Joint Venture [Member]
Contract with Customer, Liability, Total	401,300
Consolidated Construction Corporate Joint Venture [Member] | Minimum [Member]
Contract with Customer, Liability, Total	100
Consolidated Construction Corporate Joint Venture [Member] | Maximum [Member]
Contract with Customer, Liability, Total	151,800
Consolidated Construction Corporate Joint Venture [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Contract with Customer, Liability, Total	$ 711,900
Number of Active Joint Venture Projects	9
Contract Value of Active Construction Joint Venture Projects	$ 1,700,000
Revenue from Contract with Customer, Including Assessed Tax	312,500	261,200	243,100
Net Cash Provided by (Used in) Continuing Operations, Total	(3,000)	(13,100)	85,600
Consolidated Construction Corporate Joint Venture [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Minimum [Member]
Contract with Customer, Liability, Total	200
Contract Value of Active Construction Joint Venture Projects	$ 200
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 with Customer, Liability, Total	$ 253,000
Contract Value of Active Construction Joint Venture Projects	$ 434,100
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	70.00%
Line Item Joint Venture [Member]
Number of Active Joint Venture Projects	4
Unconsolidated Construction Joint Venture Net Income (Loss)	$ 318,000
Line Item Joint Venture [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Contract with Customer, Liability, Total	88,100
Contract Value of Active Construction Joint Venture Projects	187,900
Revenue from Contract with Customer, Including Assessed Tax	$ 81,300	$ 40,000	$ 4,900