Discontinued Operations Discontinued Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued operations - current assets	$ 12,743	$ 1,923	$ 12,743	$ 1,923	$ 3,057
Discontinued operations - non-current assets	0	205,081	0	205,081	10,817
Total discontinued operations assets	2,986,760	3,065,154	2,986,760	3,065,154	3,039,746
Discontinued operations - current liabilities	12,922	1,303	12,922	1,303	1,593
Discontinued operations - non-current liabilities	0	12,167	0	12,167	12,043
Total operating expenses	$ 116,298	$ 118,041	$ 312,182	$ 334,684
Income (Loss) Per Basic Share from Discontinued Operation, Net of Tax	$ (0.02)	$ (0.04)	$ (0.04)	$ (0.08)
Income (Loss) Per Diluted Share from Discontinued Operation, Net of Tax	$ (0.02)	$ (0.04)	$ (0.04)	$ (0.08)
Gill Ranch [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accounts receivable	$ 497	$ 1,130	$ 497	$ 1,130	2,126
Inventories	646	402	646	402	396
Other current assets	413	391	413	391	535
Property, Plant and Equipment, Current	10,948		10,948
Property, Plant and Equipment, Noncurrent		235,556		235,556	10,816
Discontinued Operation, Accumulated Depreciation on Property, Plant and Equipment, Current	6		6
Discontinued Operation, Accumulated Depreciation on Property, Plant and Equipment, Non-Current		30,526		30,526	0
Other non-current assets		51		51	1
Discontinued operations - current assets	12,743	1,923	12,743	1,923	3,057
Discontinued operations - non-current assets	0	205,081	0	205,081	10,817
Accounts payable	572	635	572	635	1,287
Other current liabilities	436	668	436	668	306
Other non-current liabilities		12,167		12,167	12,043
Discontinued operations - current liabilities	12,922	1,303	12,922	1,303	1,593
Discontinued operations - non-current liabilities	0	12,167	0	12,167	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	1,006	1,762	2,083	3,361
Operations and maintenance	1,554	2,251	2,590	3,921
Depreciation and amortization	108	1,131	218	2,263
Other expenses and interest	239	604	814	1,196
Total operating expenses	1,901	3,986	3,622	7,380
Loss from discontinued operations before income taxes	(895)	(2,224)	(1,539)	(4,019)
Income tax benefit	236	878	406	1,586
Loss from discontinued operations, net of tax	(659)	(1,346)	(1,133)	(2,433)
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	245		245
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	12,743	207,004	12,743	207,004	13,874
Total discontinued operations liabilities	12,922	$ 13,470	12,922	$ 13,470	$ 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	$ 11,914		$ 11,914