Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes (Textual) [Abstract]
Income taxes at a statutory rate		35.00%	35.00%
Cumulative loss period	3 years
Valuation allowance	$ 115,906	$ 177,405
Tax Cuts and Jobs Act, provisional Income tax expense (benefit)	64,900
Deferred tax assets, operating loss carryforwards	78,541	$ 92,072
Operating loss carryforwards	332,100
Operating loss carryforwards subject to expiration	6,900
Depletion Deduction
Income Taxes (Textual) [Abstract]
Depletion deduction carryforward	26,900
Louisiana
Income Taxes (Textual) [Abstract]
Operating loss carryforwards	139,400
Operating loss carryforwards subject to expiration	3,200
Accounting Standards Update 2016-09
Income Taxes (Textual) [Abstract]
Deferred tax assets, operating loss carryforwards	$ 4,700