Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued Liabilities
Accrued payroll and related employee expenses	$ 4,853	$ 4,040
Accrued employee performance bonus	3,247	7,137
Accrued Interest	5,191	5,058
Short term operating and financing leases	3,829	521
Other	3,726	7,097
Total accrued expenses	$ 20,846	$ 23,853