Long-Term Debt Credit Facility (Details) - Revolving credit facility, due April 2019		12 Months Ended
	Mar. 08, 2016 USD ($) installment	Dec. 31, 2016 USD ($) Bank	Mar. 09, 2016 USD ($)
Debt Instrument [Line Items]
Number of banks syndicated to provide for line of credit | Bank		16
Aggregate commitment amount	$ 450,000,000		$ 100,000,000
Unused capacity, commitment fee percentage	0.50%
Remaining borrowing capacity		$ 98,100,000
Letters of credit outstanding, amount		$ 1,900,000
Effective interest rate		2.50%
Federal funds rate
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
One-month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Base rate
Debt Instrument [Line Items]
Interest rate, stated percentage	0.75%
Minimum
Debt Instrument [Line Items]
Minimum ratio of discounted present value to debt	1.2
Basis spread on variable rate, additional spread	1.50%
Covenant current ratio	1
Percentage of adjusted engineered value of oil and gas interests serving as collateral	90.00%
Minimum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	2.50%
Maximum
Debt Instrument [Line Items]
Higher borrowing capacity option	$ 150,000,000
Basis spread on variable rate, additional spread	2.50%
Covenant consolidated funded indebtedness to EBI TDA ratio	2.0
Deficiency prepayment, number of equal periodic installments | installment	5
Maximum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	3.50%