Long-Term Debt and Credit Facility - Debt Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Long-term debt, term note and notes payable:
Total	$ 314,219	$ 347,312
Less – Current maturities and notes payable	29,469	26,555
Less – Unamortized loan costs	2,747	2,517
Long-term debt, less current maturities	$ 282,003	$ 318,240
Medium-term Notes
Debt Instrument [Line Items]
Debt annualized rates (as percent)	4.59%	3.60%
Long-term debt, term note and notes payable:
Term notes	$ 282,188	$ 308,437
Line of Credit
Debt Instrument [Line Items]
Debt annualized rates (as percent)	4.45%	3.50%
Long-term debt, term note and notes payable:
Line of credit, 4.45% and 3.50%, respectively	$ 31,000	$ 38,000
Notes Payable, Other Payables
Long-term debt, term note and notes payable:
Other notes with interest rates from 3.3% to 7.8%	$ 1,031	$ 875
Minimum | Notes Payable, Other Payables
Debt Instrument [Line Items]
Current stated interest rate	3.30%	3.30%
Maximum | Notes Payable, Other Payables
Debt Instrument [Line Items]
Current stated interest rate	7.80%	7.80%