Income Taxes (Schedule of Effective Tax Rate Reconciliation) (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Amount
Income tax provision calculated using the federal statutory income tax rate	$ 67,475	$ 86,086	$ 16,275
State income taxes, net of federal income tax benefit	7,435	11,968	2,764
Tax shortfall (windfall) on stock-based compensation deduction	1,912	(1,565)	5,567
Valuation allowance	26,122	(42)	5,562
Enhanced oil recovery credits generated	0	(10,818)	(11,307)
Remeasurement of deferreds related to federal tax rate change	0	0	(132,224)
Other	1,408	1,604	(3,289)
Total income tax expense (benefit)	$ 104,352	$ 87,233	$ (116,652)