Property and Equipment (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / Boe	Mar. 31, 2017 USD ($) $ / Boe	Dec. 31, 2017 USD ($)
Oil and gas properties, on the basis of full-cost accounting
Proved properties	$ 798,593		$ 765,308
Unproved properties not being amortized	7,142		7,065
Other property and equipment	6,502		6,508
Less accumulated depreciation, depletion, amortization and impairment	(219,590)		(204,419)
Net property and equipment	592,647		$ 574,462
Other information
Proceeds from the sale of oil and gas equipment		$ 1,350
Depreciation, depletion, and amortization	15,213	15,342
Oil and Gas
Other information
Internal costs capitalized to oil and gas properties	895	3,017
Capitalized qualifying share-based compensation expense	200	700
Depletion expense	14,623	14,753
Depreciation on other property and equipment	$ 590	$ 589
Depletion expense (per Boe) | $ / Boe	8.45	6.96
Depreciation on other property and equipment (per Boe) | $ / Boe	0.34	0.28
Depreciation, depletion, and amortization (per Boe) | $ / Boe	8.79	7.24
Depreciation, depletion, and amortization	$ 15,213	$ 15,342
Impairment of unproved properties	0
Oil and Gas | Anadarko Disposition | Disposed of by sale
Other information
Proceeds from the sale of oil and gas equipment	58,000
Net proceeds from the sale of oil and gas equipment	$ 1,400
Other Property and Equipment | Minimum
Other information
Estimated useful lives	2 years
Other Property and Equipment | Maximum
Other information
Estimated useful lives	10 years