Common Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands					12 Months Ended
	Feb. 14, 2018	Nov. 13, 2017	Oct. 21, 2016	Feb. 02, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Proceeds from sale of common stock		$ 302,600	$ 583,900	$ 182,800	$ 302,191	$ 766,670	$ 462,833
Common Stock
Class of Stock [Line Items]
Issuance of common stock (shares)		32,000,000	55,200,000	39,100,000
Shares issued, price per share (in usd per share)		$ 9.55	$ 10.8	$ 4.685
Common Stock | Underwriters' option
Class of Stock [Line Items]
Issuance of common stock (shares)			7,200,000	5,100,000
Common Stock
Class of Stock [Line Items]
Issuance of common stock (shares)					32,000,000	94,300,000	36,800,000
Proceeds from sale of common stock		$ 300	$ 600	$ 400
Additional Paid-in-Capital
Class of Stock [Line Items]
Proceeds from sale of common stock		$ 302,300	$ 583,300	$ 182,400
Permian Basin Acquisition | Subsequent Event | Common Stock
Class of Stock [Line Items]
Stock issued to fund portion of acquisition	46,000,000