Summary of Significant Accounting Policies - Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Asset retirement obligations
Asset retirement obligation as of beginning of period	$ 243,600	$ 168,142
Accretion expense	13,679	9,696
Liabilities incurred	19,678	2,943
Liabilities settled	(3,838)	(1,484)
Liabilities assumed in Rice Merger	50,941	0
Change in estimates	128,610	64,303
Asset retirement obligation as of end of period	$ 452,670	$ 243,600