Stock Plans - Stock Option Activity (Details) (USD$) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2012	Dec. 31, 2011
Number of shares outstanding - roll forward
Outstanding	0	0
Granted under 2011 Incentive Stock Plan	0	0		8,760	91,240
Forfeited or expired			100,000
Incentive stock plan shares authorized under 2011 Incentive Stock Plan					200,000