CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Accumulated depreciation	$ 340,423	$ 282,812
Equity
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	5,750,000	5,750,000
Preferred stock, shares outstanding	5,750,000	5,750,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	178,255,843	65,285,614
Common stock, shares outstanding	178,255,843	65,285,614