Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental disclosures:
Interest paid	$ 6	$ 0	$ 0
Income taxes paid, net	14,979	16,951	27,353
Non-cash investing and financing activities:
Non-cash capital expenditures	$ 481	$ 832	$ 270