Stock Plans (Reservation of Shares for Issuance) (Details)	Dec. 31, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total reservation of shares under stock compensation plans	3,755,930
2013 Omnibus Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total reservation of shares under stock compensation plans	3,138,321
2004 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total reservation of shares under stock compensation plans	617,609