Long-Term Debt And Other Long-Term Liabilities (Narrative) (Details) - USD ($) $ in Thousands			6 Months Ended
	May 15, 2019	May 02, 2018	Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Interest percentage of senior subordinated notes			6.625%
Debt instrument maturity date			May 15, 2021
Estimated principal payments in year 1			$ 13,900
Estimated principal payments in year 2			697,500
Estimated principal payments in year 3			5,600
Estimated principal payments in year 4			10,700
Estimated principal payments in year 5			105,800
6.625% Senior Subordinated Notes Due 2021 [Member]
Debt Instrument [Line Items]
Aggregate principal amount			$ 650,000	$ 650,000
Interest percentage of senior subordinated notes			6.625%
Senior notes repurchase price in percentage	100.00%		101.00%
Debt instrument maturity date			May 15, 2021
Original debt issuance fees			$ 14,700
Unit Credit Agreement [Member]
Debt Instrument [Line Items]
Credit facility maximum credit amount			$ 1,000,000
Commitment fee percentage under credit facility			0.375%
Origination, agency and syndication and other related fees with the credit agreement			$ 3,300
Payable assessment term for LIBOR			90 days
LIBOR interest rate plus one percent			LIBOR plus 1.00% plus a margin
Line of credit facility, amount outstanding			$ 103,500	0
Unit Credit Agreement, Dividend Restrictions			the payment of dividends (other than stock dividends) during any fiscal year over 30% of our consolidated net income for the preceding fiscal year;
Unit Credit Agreement, Asset Restrictions			investments in Unrestricted Subsidiaries (as defined in the Unit credit agreement) over $200.0 million
Current ratio of credit facility			1 to 1
Leverage ratio of credit facility			4 to 1
Covenant Compliance			As of June 30, 2019, we were in compliance with these covenants.
Unit Credit Agreement [Member] | Minimum [Member]
Debt Instrument [Line Items]
LIBOR plus interest rate			1.50%
Unit Credit Agreement [Member] | Maximum [Member]
Debt Instrument [Line Items]
LIBOR plus interest rate			2.50%
Unit Credit Agreement [Member] | Line Of Credit Facility Commitment Amount [Member]
Debt Instrument [Line Items]
Credit facility current credit amount			$ 425,000
Unit Credit Agreement [Member] | Line Of Credit Facility Lender Determined Amount [Member]
Debt Instrument [Line Items]
Credit facility current credit amount			$ 425,000
Unit Credit Agreement [Member] | Proved developed producing total value of our oil and gas properties [Member]
Debt Instrument [Line Items]
Percentage of collateral pledged			80.00%
Present worth discounted			8.00%
Superior Credit Agreement [Member]
Debt Instrument [Line Items]
Credit facility maximum credit amount			$ 250,000
Credit facility current credit amount			$ 200,000
Commitment fee percentage under credit facility			0.375%
Origination, agency and syndication and other related fees with the credit agreement			$ 1,700
Line of credit facility, amount outstanding			$ 7,500	$ 0
Covenant Compliance			As of June 30, 2019, Superior was in compliance with these covenants.
Superior Credit Agreement, Term			5 years
Superior Credit Agreement, Interest Rate Description			annual interest at a rate, at Superior’s option, equal to (a) LIBOR plus the applicable margin of 2.00% to 3.25% or (b) the alternate base rate (greater of (i) the federal funds rate plus 0.5%, (ii) the prime rate, and (iii) third day LIBOR plus 1.00%) plus the applicable margin of 1.00% to 2.25%.
Superior Credit Agreement [Member] | Minimum [Member]
Debt Instrument [Line Items]
Consolidated EBITDA to interest expense ratio			2.50 to 1.00
Superior Credit Agreement [Member] | Maximum [Member]
Debt Instrument [Line Items]
Funded debt to consolidated EBITDA ratio			4.00 to 1.00
Pledge agreement [Member] | Unit Credit Agreement [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Collateral		granting a security interest in the limited liability membership interests and other equity interests we own in Superior (which as of this report is 50% of the aggregate outstanding equity interests of Superior