Commitments and Contingencies (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2011	Sep. 30, 1999
Commitments and Contingencies
Equipment rental expense	$ 67,000	$ 67,000	$ 68,000
Contingent obligation
Contingent obligation beginning balance	1,960,000
Provision for contingent obligation	424,000	158,000	$ 75,000	$ 2,250,000
Provision for contingent obligation at period end	$ 2,384,000	1,960,000
Tax gross up for parachute payment
Commitments and Contingencies
Percentage of monthly amount paid in consideration of non-compete covenants	50.00%
Minimum | Employment, severance and noncompete
Commitments and Contingencies
Maximum contingent liability	$ 7,300,000
Minimum | Tax gross up for parachute payment
Commitments and Contingencies
Maximum contingent liability	1,000,000
Maximum | Employment, severance and noncompete
Commitments and Contingencies
Maximum contingent liability	9,100,000
Maximum | Tax gross up for parachute payment
Commitments and Contingencies
Maximum contingent liability	2,800,000
Variable Rate Tax Exempt Infrastructure Revenue Bonds | Indirect Guarantee of Indebtedness
Commitments and Contingencies
Bonds issued					$ 25,900,000
Outstanding amount	14,400,000
Balance available in the sales and incremental property tax fund	1,052,000	$ 1,479,000
Amount paid into the sales and incremental property tax fund	984,000
Debt service fee	1,411,000
Variable Rate Tax Exempt Infrastructure Revenue Bonds | Irrevocable direct-pay letter of credit
Commitments and Contingencies
Irrevocable direct-pay letter of credit issued	14,642,000
Variable Rate Tax Exempt Infrastructure Revenue Bonds | Minimum | Indirect Guarantee of Indebtedness
Commitments and Contingencies
Annual payment range	1,000,000
Variable Rate Tax Exempt Infrastructure Revenue Bonds | Maximum | Indirect Guarantee of Indebtedness
Commitments and Contingencies
Annual payment range	$ 1,600,000