CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Preferred stock Series A, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock Series A, shares authorized	10,000,000	10,000,000
Preferred stock Series A, shares issued	0	0
Preferred stock Series A, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	65,369,906	63,652,721
Common stock, shares outstanding	63,915,385	63,227,727
Treasury stock, shares	1,454,521	424,994