Business Segments (Principal Geographical Areas) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Principal Geographical Areas Information
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
Income (loss) 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
Assets		4,042,441				3,773,315				4,042,441	3,773,315
Corporate [Member]
Principal Geographical Areas Information
Income (loss) from construction operations										(54,242)	(54,559)	(47,432)
Assets	[1]	416,503				503,050				416,503	503,050
United States [Member]
Principal Geographical Areas Information
Revenues										4,694,165	4,323,471	4,000,380
Income (loss) from construction operations										128,869	268,566	238,989
Assets		3,868,449				3,612,997				3,868,449	3,612,997
Foreign and U.S. Territories [Member]
Principal Geographical Areas Information
Revenues										226,307	168,838	175,292
Income (loss) from construction operations										30,786	27,683	$ 12,265
Assets		$ 173,992				$ 160,318				$ 173,992	$ 160,318

[1] Consists principally of cash and cash equivalents and corporate transportation equipment.