Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ (148,073)	$ 412,987	$ 57,278	$ 369,516
Effective income tax rate, percent			4.40%	31.60%
Federal Statutory income tax rate, percent			21.00%	35.00%
Tax Adjustments, Settlements, and Unusual Provisions			$ 193,000
Total provision for income tax expense (benefit)			$ 500		$ 882,000