Notes Payable (Details)	Sep. 30, 2020 USD ($) installment	Dec. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)
Debt Instrument [Line Items]
Total	$ 188,086,000	$ 189,012,000
Less debt issuance costs	(1,227,000)	(3,441,000)
Long-term debt	186,859,000	185,571,000
Less current maturities	(37,873,000)	(34,873,000)
Notes payable due after one year	$ 148,986,000	150,698,000
Number of monthly installments | installment	16
Notes Payable | Equipment Notes Payable, 5.2% Due December 2022 and 2023
Debt Instrument [Line Items]
Total	$ 3,142,000	3,937,000
Interest rate	5.20%
Equipment net book value	$ 2,457,000
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	8,953,000	10,429,000
Equipment net book value	8,250,000
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	$ 3,705,000	4,333,000
Equipment net book value	3,734,000
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%
Notes Payable | Equipment Notes Payable, 5.4 Percent Due August 2025
Debt Instrument [Line Items]
Total	$ 1,561,000	0
Interest rate	5.40%
Equipment net book value	$ 1,722,000
Notes Payable | Equipment Notes Payable, 5.4 Percent Due August 2025 | Minimum
Debt Instrument [Line Items]
Monthly installments	9,000
Notes Payable | Equipment Notes Payable, 5.4 Percent Due August 2025 | Maximum
Debt Instrument [Line Items]
Monthly installments	10,000
Term Loan | Non Revolving Credit Note
Debt Instrument [Line Items]
Total	$ 5,791,000	9,900,000
Interest rate	5.90%
Equipment net book value	$ 7,012,000
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	$ 1,059,000	0
Line of Credit | 3.4% Commercial Insurance Premium | Minimum
Debt Instrument [Line Items]
Monthly installments	$ 22,000
Interest rate	3.40%
Line of Credit | 3.4% Commercial Insurance Premium | Maximum
Debt Instrument [Line Items]
Monthly installments	$ 126,000
Interest rate	0.038%
Line of Credit | 4.5% Equipment Line Of Credit
Debt Instrument [Line Items]
Total	$ 6,282,000	7,719,000
Long-term debt	$ 5,217,000
Interest rate	4.50%
Initial commitment	$ 10,000,000
Line of Credit | Syndicated Credit Facility
Debt Instrument [Line Items]
Total	157,593,000	$ 152,188,000
Line of Credit | Syndicated Credit Facility | Period 1
Debt Instrument [Line Items]
Long-term debt	1,153,000
Line of Credit | Syndicated Credit Facility | Period 2
Debt Instrument [Line Items]
Long-term debt	1,280,000
Line of Credit | Syndicated Credit Facility | Period 3
Debt Instrument [Line Items]
Long-term debt	$ 1,500,000