Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accrued Expenses and Other Current Liabilities
Payroll and related costs	$ 9,989	$ 9,607
Employee benefits	5,730	5,281
Accrued warranty	3,777	3,662
Other	8,117	4,756
Accrued expenses and other current liabilities	$ 27,613	$ 23,306