Basis of Presentation and Significant Accounting Policies Basis of Presentation and Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accounting Policies [Abstract]
Estimated lease assets and liabilities	$ 100,000		$ 100,000
Transportation expenses	$ 47,254	$ 0	$ 96,551	$ 0