Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Preferred stock, liquidation preference per share	$ 50	$ 50
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	1,379,000	1,379,000
Preferred stock, shares outstanding	1,379,000	1,379,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	629,522,000	532,186,000
Common stock, shares outstanding	629,522,000	532,186,000