Stockholders' Equity - Stock incentive plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stockholders' Equity
Number of common stock shares purchased and retired	67,555	73,453	66,829
Amount of common stock purchased and retired	$ 66,000	$ 65,000	$ 104,000
Common stock shares reserved for issuance under the 2012 Stock Incentive Plan	2,000,000
Shares available for granting options or stock awards	1,258,465
Nonvested restricted stock
Stockholders' Equity
Vesting percentage on each anniversary of the grant date	20.00%
Service period to amortize aggregate market value of the nonvested restricted stock	6 years
Number of Shares
Nonvested at the beginning of the period (in shares)	775,900
Granted (in shares)	220,500
Vested (in shares)	(183,400)
Nonvested at the end of the period (in shares)	813,000	775,900
Weighted Average Grant Date Fair Value
Nonvested at the beginning of the period (in dollars per share)	$ 1.86
Granted (in dollars per share)	0.97	$ 0.89	$ 1.52
Vested (in dollars per share)	2.60
Nonvested at the end of the period (in dollars per share)	$ 1.45	$ 1.86
Fair value of shares vested	$ 477,000	$ 608,000	$ 745,000
Compensation Expense	326,000	$ 375,000	$ 580,000
Deferred compensation cost related to nonvested restricted stock	$ 565,000
Weighted-average period to recognize deferred compensation cost related to nonvested restricted stock	3 years 3 months 18 days