Stockholders’ Equity (Details) shares in Millions	12 Months Ended
	Dec. 31, 2017 item $ / shares shares	Dec. 31, 2016 $ / shares shares
Stockholders’ Equity
Preferred stock, shares authorized	1.0	1.0
Preferred stock, par value | $ / shares	$ 0.0001	$ 0.0001
Preferred stock, shares issued	0.0	0.0
Preferred stock, shares outstanding	0.0
Common stock, shares authorized	480.0	480.0
Common stock, par value | $ / shares	$ 0.0001	$ 0.0001
Common stock, shares issued	106.3	95.7
Common stock, shares outstanding	106.3	95.7
Common Stock Warrants
Stockholders’ Equity
Common stock warrants issued and outstanding	12.1
Exercisable price | $ / shares	$ 11.50
Redemption of warrant, price per share | $ / shares	$ 0.01
Notice for redemption of warrants	30 days
Threshold price of common stock to redeem warrants | $ / shares	$ 17.50
Number of trading days within a 30-trading day period ending on the third day prior to the date on which notice of redemption is given | item	20
Number of consecutive trading day period ending on the third day prior to the date on which notice of redemption is given. | item	30
Number of warrants exercised	0.0