Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Statement of Financial Position [Abstract]
Common stock, par value	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized	120,000,000	120,000,000	120,000,000
Common stock, shares issued	67,693,586	66,260,444	66,223,957
Treasury stock, shares	471,070	495,964	498,459