Notes Payable (Details) - USD ($)	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2018
Debt Instrument [Line Items]
Total	$ 193,962,000	$ 189,012,000
Less debt issuance costs	(1,410,000)	(3,441,000)
Long-term debt	192,552,000	185,571,000
Less current maturities	(38,721,000)	(34,873,000)
Notes payable due after one year	153,831,000	150,698,000
Notes Payable | Equipment Notes Payable, 5.2% Due December 2022 and 2023
Debt Instrument [Line Items]
Total	$ 3,411,000	3,937,000
Interest rate	5.20%
Equipment net book value	$ 2,752,000
Notes Payable | Equipment Notes Payable, 5.2% Due December 2022 and 2023 | Minimum
Debt Instrument [Line Items]
Monthly installments	6,000
Notes Payable | Equipment Notes Payable, 5.2% Due December 2022 and 2023 | Maximum
Debt Instrument [Line Items]
Monthly installments	24,000
Notes Payable | Equipment Notes Payable, 5.6% to 6.8% Due March 2023 Through May 2025
Debt Instrument [Line Items]
Total	9,453,000	10,429,000
Equipment net book value	8,756,000
Notes Payable | Equipment Notes Payable, 5.6% to 6.8% Due March 2023 Through May 2025 | Minimum
Debt Instrument [Line Items]
Monthly installments	$ 1,000
Interest rate	5.60%
Notes Payable | Equipment Notes Payable, 5.6% to 6.8% Due March 2023 Through May 2025 | Maximum
Debt Instrument [Line Items]
Monthly installments	$ 39,000
Interest rate	6.80%
Notes Payable | Equipment Notes Payable, 3.9% to 6.4% Due April 2021 Through December 2024
Debt Instrument [Line Items]
Total	$ 3,917,000	4,333,000
Equipment net book value	3,386,000
Notes Payable | Equipment Notes Payable, 3.9% to 6.4% Due April 2021 Through December 2024 | Minimum
Debt Instrument [Line Items]
Monthly installments	$ 2,000
Interest rate	3.90%
Notes Payable | Equipment Notes Payable, 3.9% to 6.4% Due April 2021 Through December 2024 | Maximum
Debt Instrument [Line Items]
Monthly installments	$ 23,000
Interest rate	6.40%
Term Loan | Non Revolving Credit Note
Debt Instrument [Line Items]
Total	$ 8,641,000	9,900,000
Interest rate	5.90%
Equipment net book value	$ 7,406,000
Term Loan | Syndicated Credit Facility | Period 2
Debt Instrument [Line Items]
Long-term debt	833,000
Line of Credit | Non Revolving Credit Note
Debt Instrument [Line Items]
Initial commitment			$ 12,000,000
Line of Credit | 4.4% Commercial Insurance Premium
Debt Instrument [Line Items]
Total	0	506,000
Monthly installments	$ 169,000
Interest rate	4.40%
Line of Credit | 3.4% Commercial Insurance Premium
Debt Instrument [Line Items]
Total	$ 549,000	0
Interest rate	3.40%
Line of Credit | 3.4% Commercial Insurance Premium | Minimum
Debt Instrument [Line Items]
Monthly installments	$ 22,000
Line of Credit | 3.4% Commercial Insurance Premium | Maximum
Debt Instrument [Line Items]
Monthly installments	57,000
Line of Credit | 4.5% Equipment Line Of Credit
Debt Instrument [Line Items]
Total	6,766,000	7,719,000
Long-term debt	$ 5,689,000
Interest rate	4.50%
Initial commitment	$ 10,000,000
Line of Credit | Syndicated Credit Facility
Debt Instrument [Line Items]
Total	161,225,000	$ 152,188,000
Line of Credit | Syndicated Credit Facility | Period 1
Debt Instrument [Line Items]
Long-term debt	854,000
Line of Credit | Syndicated Credit Facility | Period 2
Debt Instrument [Line Items]
Long-term debt	1,153,000
Line of Credit | Syndicated Credit Facility | Period 3
Debt Instrument [Line Items]
Long-term debt	1,280,000
Line of Credit | Syndicated Credit Facility | Period 4
Debt Instrument [Line Items]
Long-term debt	$ 1,500,000