Discontinued Operations Discontinued Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued operations current assets	$ 12,644	$ 2,106	$ 12,644	$ 2,106	$ 3,057
Discontinued operations - non-current assets	0	204,078	0	204,078	10,817
Total discontinued operations assets	3,081,407	3,105,607	3,081,407	3,105,607	3,039,746
Discontinued operations - current liabilities	13,003	1,201	13,003	1,201	1,593
Discontinued operations - non-current liabilities	0	12,106	0	12,106	12,043
Total operating expenses	$ 97,350	$ 90,753	$ 409,532	$ 425,437
Income (Loss) Per Basic Share from Discontinued Operation, Net of Tax	$ (0.02)	$ (0.02)	$ (0.06)	$ (0.11)
Income (Loss) Per Diluted Share from Discontinued Operation, Net of Tax	$ (0.02)	$ (0.02)	$ (0.06)	$ (0.11)
Gill Ranch [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accounts receivable	$ 395	$ 1,520	$ 395	$ 1,520	2,126
Inventories	661	415	661	415	396
Other current assets	107	171	107	171	535
Property, Plant and Equipment, Current	11,241		11,241
Property, Plant and Equipment, Noncurrent		235,578		235,578	10,816
Discontinued Operation, Accumulated Depreciation on Property, Plant and Equipment, Current	7		7
Discontinued Operation, Accumulated Depreciation on Property, Plant and Equipment, Non-Current		31,551		31,551	0
Other non-current assets		51		51	1
Discontinued operations current assets	12,644	2,106	12,644	2,106	3,057
Discontinued operations - non-current assets	0	204,078	0	204,078	10,817
Accounts payable	751	353	751	353	1,287
Other current liabilities	405	848	405	848	306
Other non-current liabilities		12,106		12,106	12,043
Discontinued operations - current liabilities	13,003	1,201	13,003	1,201	1,593
Discontinued operations - non-current liabilities	0	12,106	0	12,106	12,043
Gill Ranch [Member] | Discontinued Operations, Held-for-sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	748	1,977	2,831	5,338
Operations and maintenance	1,549	1,248	4,139	5,169
Depreciation and amortization	106	1,131	324	3,394
Other Income	(24)
Other expenses and interest		603	790	1,799
Total operating expenses	1,631	2,982	5,253	10,362
Loss from discontinued operations before income taxes	(883)	(1,005)	(2,422)	(5,024)
Income tax benefit	233	397	639	1,983
Loss from discontinued operations, net of tax	(650)	(608)	(1,783)	(3,041)
Gill Ranch [Member] | Non-Current Assets Held-for-Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other current assets	247		247
Gill Ranch [Member] | Discontinued Operations, Held-for-sale or Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total discontinued operations assets	12,644	206,184	12,644	206,184	13,874
Total discontinued operations liabilities	13,003	$ 13,307	13,003	$ 13,307	$ 13,636
Gill Ranch [Member] | Non-Current Liabilities Held-for-Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other current liabilities	$ 11,847		$ 11,847