Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash paid for interest	$ 109	$ 22	$ 2
Cash paid for federal and state income taxes	787	459	2,589
Non-cash transactions:
Change in accounts payable related to property and equipment additions	1,685	70	679
Property and equipment acquired under capital leases	$ 2,898	$ 1,808	$ 0