Noncontrolling Interests (Details) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016 USD ($) item	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Noncontrolling Interests
Number of joint ventures | item	2												2
Revenues	$ 601,863	$ 507,828	$ 456,811	$ 430,446	$ 497,145	$ 555,945	$ 483,545	$ 392,780	$ 487,592	$ 613,237	$ 515,291	$ 470,074	$ 1,996,948	$ 1,929,415	$ 2,086,194
Net income attributable to noncontrolling interests													1,002	279	526
Tax effect on income recognized													21,146	23,946	38,646
Distributions to non-controlling interests														29	$ 1,590
Accounts receivable	388,000				320,588								388,000	320,588
Costs and estimated earnings in excess of billings	138,618				116,455								138,618	116,455
Billings in excess of costs and estimated earnings	112,606				139,875								112,606	139,875
Current liabilities	$ 449,938				416,173								$ 449,938	416,173
Blythe | Primary beneficiary
Noncontrolling Interests
Revenues														119
Carlsbad
Noncontrolling Interests
Ownership percentage	50.00%												50.00%
Carlsbad | Primary beneficiary
Noncontrolling Interests
Revenues													$ 7,254	2,887
Net income attributable to noncontrolling interests													325	172
Distributions to partners													0
Capital contributions													0
Cash	$ 4,630				1,952								4,630	1,952
Accounts receivable					955									955
Costs and estimated earnings in excess of billings	124												124
Billings in excess of costs and estimated earnings	3,426				1,311								3,426	1,311
Current liabilities	$ 332				1,251								$ 332	1,251
Wilmington
Noncontrolling Interests
Ownership percentage	50.00%												50.00%
Billings in excess of costs and estimated earnings	$ 2,572				2,978								$ 2,572	2,978
Wilmington | Primary beneficiary
Noncontrolling Interests
Revenues													19,781	1,364
Net income attributable to noncontrolling interests													676	48
Distributions to partners													0
Capital contributions													0
Cash	2,415				2,339								2,415	2,339
Accounts receivable	4,242				2,003								4,242	2,003
Current liabilities	$ 2,637				$ 1,269								$ 2,637	$ 1,269