Debt - Summary of total debt (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Total debt	$ 81,968	$ 165,824
Less: current portion of long-term debt	(7,186)	(8,737)
Long-term debt	74,782	157,087
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Total debt	$ 48,571	62,004
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Term (years)	5 years
Total debt	$ 33,397	103,820
Equipment Note One [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Stated Interest Rate (per annum)	4.16%
Term (years)	5 years
Total debt	$ 0	10,643
Equipment Note Two [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Stated Interest Rate (per annum)	4.23%
Term (years)	7 years
Total debt	$ 10,643	11,200
Equipment Note Three [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Stated Interest Rate (per annum)	3.97%
Term (years)	5 years
Total debt	$ 1,779	1,953
Equipment Note Four [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Stated Interest Rate (per annum)	4.02%
Term (years)	7 years
Total debt	$ 2,003	2,108
Equipment Note Five [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Stated Interest Rate (per annum)	4.01%
Term (years)	7 years
Total debt	$ 1,649	1,751
Equipment Note Six [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Stated Interest Rate (per annum)	2.89%
Term (years)	7 years
Total debt	$ 13,596	14,286
Equipment Note Seven [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Stated Interest Rate (per annum)	3.09%
Term (years)	5 years
Total debt	$ 8,359	9,033
Equipment Note Eight [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Stated Interest Rate (per annum)	2.75%
Term (years)	5 years
Total debt	$ 6,008	6,496
Equipment Note Nine [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Stated Interest Rate (per annum)	3.01%
Term (years)	7 years
Total debt	$ 4,534	$ 4,534

Contractual interest rate for funds borrowed, under the debt agreement.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
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-Publisher FASB
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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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