Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred tax liabilities [Abstract]
Hedge contracts	$ 0	$ 9,578	$ 8,114
Assets held for sale	3,390	0	0
Deferred Tax Liabilities, Other	4,431	4,042	4,458
Total deferred tax liabilities	7,821	13,620	12,572
Deferred tax assets [Abstract]
U.S. full cost pool	48,436	35,689	3,352
Deferred Tax Assets, Capital Loss Carryforwards	7,361	7,767	12,325
Depletion carryforward	5,216	5,558	4,936
U.S. net operating loss carryforward	80,670	67,531	50,941
Alternative minimum tax credit	757	757	1,104
Hedge contracts	3,135	0	0
Total deferred tax assets	145,575	117,302	72,658
Valuation allowance for deferred tax assets	(137,754)	(103,682)	(60,086)
Net deferred tax assets	7,821	13,620	12,572
Net deferred tax	0	0	0
Current [Abstract]
Federal	0	(242)	(276)
State	0	(37)	(11)
Current provision (benefit) for income taxes	0	(279)	(287)
Deferred [Abstract]
Federal	0	0	0
Deferred provision (benefit) for income taxes	0	0	0
Reconciliation of income tax computed at U.S federal statutory tax rates [Abstract]
Tax (expense) benefit at U.S. statutory rates (35%)	33,732	44,586	(22,044)
(Increase) decrease in deferred tax asset valuation allowance	(34,072)	(43,596)	15,480
Alternative minimum tax	0	568	0
Rate differential for non US income	0	0	(39)
State income taxes	0	0	0
Accrual of prior year federal taxes (2009)	0	37	287
Permanent differences	(1,133)	(1,371)	(950)
Return to provision estimate revision	1,473	0	4,562
Tax benefit related to the sale of Canadian subsidiary	0	0	3,501
Increase in asset for partnership distributions	0	0	0
Other	0	55	(510)
Income tax (expense) benefit	$ 0	$ 279	$ 287
U.S statutory rate (in hundredths)	35.00%
Reduction in deferred tax assets	$ 28,300
U.S. Tax [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 230,500
Expiration dates of operating loss carryforwards	Dec. 31, 2036