Income Taxes - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
State tax effected net operating losses
Tax benefit attributable to tax reform		$ 242,875	$ 0	$ 0
Effective tax rate		143.95%	36.76%	39.18%
Alternative minimum tax credits	$ 208,624	$ 208,624	$ 218,773
Unrecognized tax benefits	700	700
Federal
State tax effected net operating losses
Net operating loss carryforwards	839,300	839,300
State Tax Reporting
State tax effected net operating losses
Net operating loss carryforwards	543,700	543,700
Valuation allowance on operating loss carryforwards	5,000	$ 5,000
Refundable Portion Of AMT Credits
State tax effected net operating losses
Valuation allowance recorded	$ 10,700
Previously reported
State tax effected net operating losses
Effective tax rate		37.60%