Significant Accounting Policies (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Use of and Changes in Estimates
Income from construction operations	$ 65,443,000	$ 39,474,000	$ 106,940,000	$ 75,553,000
Net income	28,545,000	15,478,000	44,484,000	30,278,000
Diluted earnings per common share (in dollars per share)	$ 0.58	$ 0.32	$ 0.91	$ 0.62
Increase decrease in the estimated recovery projected for two projects
Use of and Changes in Estimates
Number of projects impacted by change in the estimated recoveries	2
Favorable increase in results of operations	24,200,000
Unfavorable decrease in results of operations	9,400,000
Income from construction operations	14,800,000		14,800,000
Net income	$ 8,800,000		$ 8,800,000
Diluted earnings per common share (in dollars per share)	$ 0.18		$ 0.18