Shareholders' Equity - Summary of Share Count and Par Value Data Related to Shareholders' Equity (Details) - $ / shares	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Preferred Stock
Preferred stock, par value per share
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares outstanding	0	0
Common Stock
Common stock, par value per share
Common stock, shares authorized	75,000,000	75,000,000
Common stock, shares issued	56,781,065	56,632,488
Common stock, shares outstanding	33,087,043	32,938,466	32,933,326	32,762,494
Treasury stock
Treasury stock, shares held	23,694,022	23,694,022