Summary of Significant Accounting Policies - Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net loss per share
Potentially dilutive common shares not been included in net loss per common share calculations because the effect would have been anti-dilutive	869,684	730,192	684,581
Stock options
Net loss per share
Potentially dilutive common shares not been included in net loss per common share calculations because the effect would have been anti-dilutive	866,132	723,747	681,248
Restricted Stock
Net loss per share
Potentially dilutive common shares not been included in net loss per common share calculations because the effect would have been anti-dilutive	3,552	6,445	3,333