Supplemental Cash Flow Information - Cash Payments and Non-Cash Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental cash flow information:
Cash paid for interest	$ 9	$ 28	$ 55
Cash paid for income taxes	2,488	2,576	4,682
Supplemental noncash investing and financing activities:
Transfer of service and sales demonstration inventory to fixed assets	$ 2,844	$ 511	$ 2,979