Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes (Textual) [Abstract]
Income taxes at a statutory rate		35.00%	35.00%
Cumulative loss period	3 years
Valuation allowance	$ 118,716	$ 115,906
Tax Cuts and Jobs Act, provisional Income tax expense (benefit)		64,900
Deferred tax assets, operating loss carryforwards	86,046	78,541
Operating loss carryforwards	355,400
Operating loss carryforwards, not subject to expiration, subject to limitation	20,300
Depletion Deduction
Income Taxes (Textual) [Abstract]
Tax credit carryforward	28,200
Deductible Interest Expense [Member]
Income Taxes (Textual) [Abstract]
Tax credit carryforward	43,900
Louisiana
Income Taxes (Textual) [Abstract]
Operating loss carryforwards	180,700
Operating loss carryforwards subject to expiration	300
Accounting Standards Update 2016-09
Income Taxes (Textual) [Abstract]
Deferred tax assets, operating loss carryforwards		$ 4,700
Tax Year 2025
Income Taxes (Textual) [Abstract]
Operating loss carryforwards subject to expiration	6,900
Tax Year 2037
Income Taxes (Textual) [Abstract]
Operating loss carryforwards subject to expiration	$ 328,200