Unaudited Quarterly Financial Data (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares	Sep. 30, 2015 USD ($) $ / shares	Jun. 30, 2015 USD ($) $ / shares	Mar. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($) $ / shares	Sep. 30, 2014 USD ($) $ / shares	Jun. 30, 2014 USD ($) $ / shares	Mar. 31, 2014 USD ($) $ / shares	Dec. 31, 2015 USD ($) segment $ / shares	Dec. 31, 2014 USD ($) $ / shares	Dec. 31, 2013 USD ($) $ / shares
Quarterly Financial Data [Line Items]
Revenues	$ 1,200,830	$ 1,340,739	$ 1,312,438	$ 1,066,465	$ 1,201,877	$ 1,250,689	$ 1,084,510	$ 955,233	$ 4,920,472	$ 4,492,309	$ 4,175,672
Gross profit	66,673	100,201	98,620	90,759	129,723	140,841	129,531	105,347	356,253	505,442	466,904
Income from construction operations	15,474	38,974	30,881	20,084	64,396	70,354	65,443	41,497	105,413	241,690	203,822
Income before income taxes	11,687	33,955	19,992	8,205	53,917	58,616	47,612	27,293	73,839	187,438	139,615
Net income	$ 8,712	$ 19,677	$ 11,777	$ 5,126	$ 27,722	$ 35,730	$ 28,545	$ 15,939	$ 45,292	$ 107,936	$ 87,296
Earnings per share:
Net income (loss) per share: Basic | $ / shares	$ 0.18	$ 0.40	$ 0.24	$ 0.11	$ 0.57	$ 0.74	$ 0.59	$ 0.33	$ 0.92	$ 2.22	$ 1.82
Diluted (in dollars per share) | $ / shares	$ 0.18	$ 0.40	$ 0.24	$ 0.10	$ 0.56	$ 0.73	$ 0.58	$ 0.33	$ 0.91	$ 2.20	$ 1.80
Number of Operating Segments | segment									3