Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	42,563,808	41,627,103
Common stock, shares outstanding	34,189,599	35,048,338
Treasury stock, shares	8,374,209	6,578,765