Common Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Oct. 21, 2016	Feb. 02, 2016	Mar. 09, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Proceeds from sale of common stock	$ 583,900	$ 182,800	$ 462,800	$ 766,670	$ 462,833	$ 0
Common stock
Class of Stock [Line Items]
Issuance of common stock (shares)	55,200,000	39,100,000	36,800,000
Shares issued, price per share (in usd per share)	$ 10.80	$ 4.685	$ 12.80
Common stock | Underwriters' option
Class of Stock [Line Items]
Issuance of common stock (shares)	7,200,000	5,100,000	4,800,000
Common stock
Class of Stock [Line Items]
Issuance of common stock (shares)				94,300,000	36,800,000	0
Proceeds from sale of common stock	$ 600	$ 400	$ 400
Additional paid-in capital
Class of Stock [Line Items]
Proceeds from sale of common stock	$ 583,300	$ 182,400	$ 462,400