Long-Term Debt and Credit Facility - Debt Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Long-term debt, term note and notes payable:
Total	$ 347,312	$ 374,026
Less – Current maturities and notes payable	26,555	19,835
Debt Issuance Costs, Net	2,517	3,406
Long-term debt, less current maturities	$ 318,240	$ 350,785
Medium-term Notes
Debt Instrument [Line Items]
Debt annualized rates (as percent)	3.60%	3.08%
Long-term debt, term note and notes payable:
Term notes	$ 308,437	$ 328,125
Line of Credit
Debt Instrument [Line Items]
Debt annualized rates (as percent)	3.50%	2.96%
Long-term debt, term note and notes payable:
Line of credit, 3.50% and 2.96%, respectively	$ 38,000	$ 36,000
Notes Payable, Other Payables
Long-term debt, term note and notes payable:
Other notes with interest rates from 3.3% to 7.8%	$ 875	$ 9,901
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%