Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Undesignated preferred stock, par value	$ 0.01	$ 0.01
Undesignated preferred stock, shares authorized	10,000,000	10,000,000
Undesignated preferred stock, shares issued	0	0
Undesignated preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	280,000,000	280,000,000
Common stock, shares issued	187,029,967	119,053,414
Common stock, shares outstanding	187,029,967	119,053,414