Debt - Schedule of remaining principal payments for long term obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Long-term Debt Outstanding Balance	$ 89,792	$ 78,960
Less: Current portion of equipment notes	(3,681)	0
Long-term principal obligations	86,111	78,960
Notes Payable to Banks [Member]
Long-term Debt Outstanding Balance	31,486	$ 0
Master Loan Agreement [Member] \| Notes Payable to Banks [Member]
2019	3,681
2020	3,835
2021	3,996
2022	4,163
2023	7,327
Thereafter	8,484
Long-term Debt Outstanding Balance	31,486
Less: Current portion of equipment notes	(3,681)
Long-term principal obligations	$ 27,805

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.

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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 of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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