Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 49,095	$ (160,841)	$ 205,351	$ (43,471)
Effective income tax rate, percent			19.68%	23.90%
Federal Statutory income tax rate, percent			21.00%	35.00%
Total provision for income tax expense (benefit)					$ 882,000