Stock Compensation (Schedule of Share-Based Compensation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expensed	$ 11,951	$ 15,154	$ 14,995
Stock-based compensation capitalized	3,487	4,567	6,047
Total cost of stock-based compensation arrangements	15,438	19,721	21,042
Income tax benefit recognized for stock-based compensation arrangements	2,988	5,759	5,698
General and administrative expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expensed	11,951	15,154	14,359
Lease operating expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expensed	$ 0	$ 0	$ 636