Stock Compensation Plans (Schedule of Share-Based Compensation) (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total compensation expenses	$ 29,310	$ 33,190	$ 36,091
Stock-based compensation capitalized	8,587	6,998	3,702
Total Cost Of Stock Based Compensation Arrangements	37,897	40,188	39,793
Income tax benefit recognized for stock-based compensation arrangements	15,131	18,383	8,462
General and Administrative Expense [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total compensation expenses	26,463	30,256	28,169
Lease Operating Expense [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total compensation expenses	2,847	2,621	2,056
Encore Merger Expense [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total compensation expenses	$ 0	$ 313	$ 5,866