Line of Credit and Long-Term Debt - Additional Information (Details)	3 Months Ended	9 Months Ended
	Sep. 30, 2013 USD ($)	Sep. 30, 2018 USD ($) covenant	Dec. 31, 2017 USD ($)
Promissory note agreement
Line of Credit Facility [Line Items]
Debt instrument face amount	$ 4,750,000
Stated interest rate	4.25%
Periodic principal and interest payments	$ 102,700
Long-term debt		$ 3,488,000
Level 2 | Interest Rate Swap
Line of Credit Facility [Line Items]
Notional Amount		$ 63,393,000	$ 66,046,000
Interest pay rate		4.11%
Selected LIBOR rate
Line of Credit Facility [Line Items]
Interest rate on line of credit, variable rate		1.50%
LIBOR for a fixed rate term
Line of Credit Facility [Line Items]
Interest rate on line of credit, variable rate		1.50%
Term Notes
Line of Credit Facility [Line Items]
Line of credit amount		$ 70,000,000
Interest pay rate		4.11%
Periodic payments, interest only period		2 years
Term Notes | Selected LIBOR rate
Line of Credit Facility [Line Items]
Interest rate on line of credit, variable rate		1.70%
Revolving line of credit
Line of Credit Facility [Line Items]
Line of credit amount		$ 30,000,000
Commitment fee percentage		0.10%
Number of debt covenants | covenant		3
Debt equity ratio		0.75
Debt service coverage ratio		1.25
Minimum liquid assets		$ 20,000,000