Unaudited Quarterly Financial Data (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Jun. 30, 2016 USD ($) $ / shares	Mar. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares	Sep. 30, 2015 USD ($) $ / shares	Jun. 30, 2015 USD ($) $ / shares	Mar. 31, 2015 USD ($) $ / shares	Dec. 31, 2016 USD ($) segment $ / shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($) $ / shares
Unaudited Quarterly Financial Data [Abstract]
Revenues	$ 1,246,599	$ 1,332,978	$ 1,308,130	$ 1,085,369	$ 1,200,830	$ 1,340,739	$ 1,312,438	$ 1,066,465	$ 4,973,076	$ 4,920,472	$ 4,492,309
Gross profit	117,660	124,668	109,770	105,092	66,673	100,201	98,620	90,759	457,190	356,253	505,442
Income from construction operations	52,050	60,919	48,829	40,122	15,474	38,974	30,881	20,084	201,920	105,413	241,690
Income before income taxes	38,685	47,926	35,780	26,724	11,687	33,955	19,992	8,205	149,115	73,839	187,438
Net income	$ 30,260	$ 28,801	$ 21,361	$ 15,400	$ 8,712	$ 19,677	$ 11,777	$ 5,126	$ 95,822	$ 45,292	$ 107,936
Earnings per share:
Net income per share: Basic | $ / shares	$ 0.62	$ 0.59	$ 0.43	$ 0.31	$ 0.18	$ 0.40	$ 0.24	$ 0.11	$ 1.95	$ 0.92	$ 2.22
Diluted (in dollars per share) | $ / shares	$ 0.60	$ 0.57	$ 0.43	$ 0.31	$ 0.18	$ 0.40	$ 0.24	$ 0.10	$ 1.92	$ 0.91	$ 2.20
Number of Operating Segments | segment									3