Business Segments (Reconciliation of Segment Results to Consolidated Income Before Income Taxes) (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
Business Segments [Abstract]
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
Other income (expense), net									12,453	(9,536)	(18,575)
Interest expense									(44,027)	(44,716)	(45,632)
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