Other Current Assets and Other Assets - Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Other Current Assets and Other Assets
Non-trade receivables	$ 6,711		$ 7,848
Prepaid maintenance	2,767		3,330
Prepaid rent	1,145		4,442
Prepaid other	994		1,101
Prepaid purchase orders	922		998
Prepaid education and training	726		597
Prepaid insurance	264		258
Other	144		157
Total other current assets	$ 13,673	$ 12,961	$ 18,731