Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Non-cash investing and financing activities:
Purchase of property, plant, and equipment in accounts payable	$ 4,522	$ 4,364	$ 1,784
Additional cash payment information:
Interest paid	1,489	1,467	818
Income taxes paid	$ 13,526	$ 16,409	$ 9,393