Supplemental Cash Flow Information - Cash Payments and Non-Cash Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental cash flow information:
Cash paid for interest	$ 4	$ 9	$ 28
Cash paid for income taxes	5,813	2,488	2,576
Supplemental noncash investing and financing activities:
Transfer of service and sales demonstration inventory to fixed assets	$ 964	$ 2,844	$ 511