Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenue, Net	$ 171,852	$ 166,247	$ 163,903	$ 157,807	$ 149,542	$ 143,483	$ 148,069	$ 153,647	$ 659,809	$ 594,741	$ 797,520
Revenues									0	0	0
Income Before Interest Expense and Taxes	32,378	$ 27,476	$ 29,407	$ 23,179	21,524	$ 21,488	$ 20,227	$ 22,940	112,440	86,179	161,070
Assets	584,812				573,052				584,812	573,052	625,258
Payments to Acquire Property, Plant, and Equipment									18,775	11,356	22,797
Depreciation and amortization									24,940	26,872	27,457
Operating Segment Reservoir Description [Member]
Segment Reporting Information [Line Items]
Revenue, Net									415,220	426,205	514,845
Revenues									294	784	584
Income Before Interest Expense and Taxes									66,500	78,881	123,505
Assets	320,569				316,801				320,569	316,801	347,600
Payments to Acquire Property, Plant, and Equipment									10,406	8,220	17,939
Depreciation and amortization									17,972	18,494	17,696
Operating Segment Production Enhancement [Member]
Segment Reporting Information [Line Items]
Revenue, Net									244,589	168,536	282,675
Revenues									1,185	877	1,981
Income Before Interest Expense and Taxes									46,459	7,198	38,210
Assets	206,389				195,104				206,389	195,104	215,872
Payments to Acquire Property, Plant, and Equipment									6,819	2,298	3,475
Depreciation and amortization									4,851	5,856	7,317
Operating Segment Corporate And Other [Member]
Segment Reporting Information [Line Items]
Revenue, Net									0	0	0
Revenues									(1,479)	(1,661)	(2,565)
Income Before Interest Expense and Taxes									(519)	100	(645)
Assets	$ 57,854				$ 61,147				57,854	61,147	61,786
Payments to Acquire Property, Plant, and Equipment									1,550	838	1,383
Depreciation and amortization									$ 2,117	$ 2,522	$ 2,444