Description of Business and Summary of Significant Accounting Policies (Narrative) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 segment	Dec. 31, 2013	Dec. 31, 2012
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Number of reportable segments									3
Income from construction operations	$ 64,396,000	$ 70,354,000	$ 65,443,000	$ 41,497,000	$ 70,175,000	$ 58,094,000	$ 39,474,000	$ 36,079,000	$ 241,690,000	$ 203,822,000	$ (221,811,000)
Net income	27,722,000	35,730,000	28,545,000	15,939,000	33,259,000	23,759,000	15,478,000	14,800,000	107,936,000	87,296,000	(265,400,000)
Diluted earnings per common share (in dollars per share)	$ 0.56	$ 0.73	$ 0.58	$ 0.33	$ 0.68	$ 0.49	$ 0.32	$ 0.31	$ 2.20	$ 1.80	$ (5.59)
Unapproved change orders and claims subject to pending litigation	38,400,000				58,800,000				38,400,000	58,800,000
Costs and estimated earnings in excess of billings beyond one year	251,300,000								251,300,000
Increase In The Estimated Recovery Projected For Civil and Building Segment Projects [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Impact on results of operations									27,900,000
Income from construction operations									27,900,000
Net income									16,000,000
Diluted earnings per common share (in dollars per share)									$ 0.33
Increase In The Estimated Recovery Projected For Civil Segment Project [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Number of reportable segments			2
Impact on results of operations (increase)									25,900,000
Impact on results of operations (decrease)									9,400,000
Increase In The Estimated Recovery Projected For Building Segment Project [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Impact on results of operations	11,400,000									13,800,000
Income from construction operations										13,800,000
Net income										8,600,000
Diluted earnings per common share (in dollars per share)										$ 0.18
Minimum [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Span of larger contracts									2 years
Fair value inputs, discount rate (in hundredths)									14.00%
Minimum [Member] | Construction Equipment [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives									5 years
Minimum [Member] | Remaining Depreciable Property [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives									3 years
Maximum [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Span of larger contracts									6 years
Fair value inputs, discount rate (in hundredths)									18.00%
Maximum [Member] | Construction Equipment [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives									20 years
Maximum [Member] | Remaining Depreciable Property [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives									40 years
Income Approach Valuation Model [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Weight assumed for calculating fair value of reporting units	67.00%								67.00%
Market-based Approach [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Weight assumed for calculating fair value of reporting units	33.00%								33.00%
Stock Options [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Antidilutive securities excluded from computation of diluted earnings per share									9,000	860,000	1,315,465
Restricted Stock Units [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Antidilutive securities excluded from computation of diluted earnings per share											1,291,665
ARS [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Investment in ARS classified as available-for-sale	46,283,000				46,283,000				46,283,000	46,283,000	46,283,000
ARS settlements									44,497,000
Realized loss included in other income (expense), net									$ (1,786,000)
ARS [Member] | Income Approach Valuation Model [Member] | Minimum [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Fair value inputs, discount rate (in hundredths)									3.00%
Fair value inputs, term of auction rate securities									6 years
ARS [Member] | Income Approach Valuation Model [Member] | Maximum [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Fair value inputs, discount rate (in hundredths)									7.00%
Fair value inputs, term of auction rate securities									8 years