Line of Credit and Long-Term Debt - Additional Information (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) covenant	Dec. 31, 2013 USD ($)	Dec. 31, 2018 USD ($)
Line of Credit Facility [Line Items]
RLC outstanding balance	$ 64,908,000		$ 65,915,000
Interest pay rate	4.11%
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		$ 36,000
Long-term debt	$ 3,347,000
Level 2 | Interest Rate Swap
Line of Credit Facility [Line Items]
Notional Amount	$ 61,561,000		62,483,000
Interest pay rate	4.11%
Term Notes
Line of Credit Facility [Line Items]
Line of credit amount	$ 70,000,000
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%
RLC outstanding balance	$ 0		$ 0
Number of debt covenants | covenant	3
Debt equity ratio	0.75
Debt service coverage ratio	1.25
Minimum liquid assets	$ 20,000,000
Revolving line of credit | Selected LIBOR rate
Line of Credit Facility [Line Items]
Interest rate on line of credit, variable rate	1.50%
Revolving line of credit | LIBOR for a fixed rate term
Line of Credit Facility [Line Items]
Interest rate on line of credit, variable rate	1.50%