Statement Of Cash Flow Information - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Information [Abstract]
Interest paid, net of interest capitalized	$ 10,367	$ 18,749	$ 14,555
Income taxes paid	$ 6,015	$ 5,635	$ 16,905