Revenue from Contracts with Customers Revenue from Contracts with Customers (Revenue Impact of the Adoption of ASC606) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Adoption of ASC606 [Line Items]
Oil and natural gas revenues	$ 103,099	$ 87,598
Oil and natural gas operating costs	35,962	29,204
Oil and natural gas gross profit	67,137
Gas gathering and processing	56,044	50,941
Deferred tax expense	3,607	13,936
Net income	7,865	$ 15,929
Adjustments due to ASC606 [Member]
Adoption of ASC606 [Line Items]
Oil and natural gas revenues	(3,169)
Oil and natural gas operating costs	(3,169)
Oil and natural gas gross profit	0
Gas gathering and processing	1,192
Deferred tax expense	292
Net income	900
Amounts without the Adoption of ASC606 [Member]
Adoption of ASC606 [Line Items]
Oil and natural gas revenues	106,268
Oil and natural gas operating costs	39,131
Oil and natural gas gross profit	67,137
Gas gathering and processing	54,852
Deferred tax expense	3,315
Net income	$ 6,965