Stockholders' Equity - Stock incentive plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014
Stockholders Equity
Maximum number of shares authorized for grant				2,000,000
Number of shares available for granting options or stock awards	1,440,730
Restricted Stock
Stockholders Equity
Vesting rights percentage each year beginning on the second anniversary date of the grant				20.00%
Service period over which the aggregate market value of stock is being amortized	6 years			6 years
Number of Shares
Nonvested at the beginning of the period (in shares)	583,000
Granted (in shares)	151,000
Vested (in shares)	(141,200)
Nonvested at the end of the period (in shares)	592,800	583,000
Weighted Average Grant Date Fair Value
Nonvested at the beginning of the period (in dollars per share)	$ 2.25
Granted (in dollars per share)	2.00	$ 2.27	$ 2.33
Vested (in dollars per share)	2.04
Nonvested at the end of the period (in dollars per share)	$ 2.24	$ 2.25
Additional disclosure
Total fair value of shares vested during the period (in dollars)	$ 288,000	$ 267,000	$ 261,000
Stock-based compensation expense	302,000	$ 364,000	$ 284,000
Total unrecognized compensation cost (in dollars)	$ 691,000
Weighted-average period for recognition of total unrecognized compensation cost	3 years 8 months 12 days