Business Segments (Reconciliation of Segment Results to Consolidated Income Before Income Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Segments [Abstract]
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
Other income (expense), net									6,977	13,569	(8,217)
Interest expense									(59,782)	(45,143)	(46,035)
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