Business Segments (Principal Geographical Areas) (Details) (USD $) In Thousands, unless otherwise specified	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	Dec. 31, 2013	Dec. 31, 2012
Principal Geographical Areas Information
Revenues	$ 1,201,877	$ 1,250,689	$ 1,084,510	$ 955,233	$ 1,099,291	$ 1,030,388	$ 1,053,065	$ 992,928	$ 4,492,309	$ 4,175,672	$ 4,111,471
Income (loss) from construction operations	64,396	70,354	65,443	41,497	70,175	58,094	39,474	36,079	241,690	203,822	(221,811)
Assets	3,773,315				3,397,438				3,773,315	3,397,438	3,296,410
Corporate [Member]
Principal Geographical Areas Information
Income (loss) from construction operations									(54,559)	(47,432)	(45,094)
Assets	503,050				576,127				503,050	576,127	727,699
United States | Reportable Geographical Components
Principal Geographical Areas Information
Revenues									4,323,471	4,000,380	3,925,733
Income (loss) from construction operations									268,566	238,989	(195,457)
Assets	3,612,997				3,182,706				3,612,997	3,182,706	3,107,808
Foreign and U.S. Territories | Reportable Geographical Components
Principal Geographical Areas Information
Revenues									168,838	175,292	185,738
Income (loss) from construction operations									27,683	12,265	18,740
Assets	$ 160,318				$ 214,732				$ 160,318	$ 214,732	$ 188,602