Debt - Schedule of Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2013
Principal Balances
Total debt	$ 36,702	$ 89,094
Less amounts due within one year	(6,110)	(56,097)
Total long-term debt	30,592	32,997
Unamortized Debt Financing Costs
Total debt	160	209
Less amounts due within one year	(67)	(84)
Total long-term debt	93	125
Balance, Net of Financing Costs
Total debt	36,542	88,885
Less amounts due within one year	(6,043)	(56,013)
Total long-term debt	30,499	32,872
7.5% Notes
Principal Balances
Total debt		50,000
Unamortized Debt Financing Costs
Total debt		17
Balance, Net of Financing Costs
Total debt		$ 49,983
Interest rate		7.50%	7.50%
NG Advantage debt
Principal Balances
Total debt	31,489	$ 33,898
Unamortized Debt Financing Costs
Total debt	160	192
Balance, Net of Financing Costs
Total debt	31,329	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	613	796
Balance, Net of Financing Costs
Total debt	$ 613	$ 796