Debt - Schedule of Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2013
Principal Balances
Total debt	$ 87,771	$ 89,094
Less amounts due within one year	(56,104)	(56,097)
Total long-term debt	31,667	32,997
Unamortized Debt Financing Costs
Total debt	183	209
Less amounts due within one year	(74)	(84)
Total long-term debt	109	125
Balance, Net of Financing Costs
Total debt	87,588	88,885
Less amounts due within one year	(56,030)	(56,013)
Total long-term debt	31,558	32,872
7.5% Notes
Principal Balances
Total debt	50,000	50,000
Unamortized Debt Financing Costs
Total debt	8	17
Balance, Net of Financing Costs
Total debt	$ 49,992	$ 49,983
Interest rate	7.50%	7.50%	7.50%
NG Advantage debt
Principal Balances
Total debt	$ 32,434	$ 33,898
Unamortized Debt Financing Costs
Total debt	175	192
Balance, Net of Financing Costs
Total debt	32,259	33,706
SG Facility
Principal Balances
Total debt	4,600	4,400
Balance, Net of Financing Costs
Total debt	4,600	4,400
Other debt
Principal Balances
Total debt	737	796
Balance, Net of Financing Costs
Total debt	$ 737	$ 796