Business Segments Reconciliation of Segment Information to Consolidated Amounts (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting [Abstract]
Income from construction operations	$ 74,400	$ 83,021	$ 57,696	$ 47,227	$ (94,146)	$ 47,943	$ (341,717)	$ 22,913	$ 262,344	$ (365,007)	$ 191,876
Other income (expense)									(11,853)	6,667	4,256
Interest expense									(76,212)	(67,494)	(63,519)
Income (loss) before income taxes	$ 53,212	$ 49,360	$ 40,435	$ 31,272	$ (106,717)	$ 32,312	$ (358,339)	$ 6,910	$ 174,279	$ (425,834)	$ 132,613