Supplemental Discloure of Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Interest Paid, Net	$ 0	$ 0	$ 0
Income Taxes Paid	14,050	13,670	11,261
Noncash or Part Noncash Acquisition, Inventory Acquired from Affiliates	0	0	747
Contribution of Property	0	798	18,828
Contribution of Real Estate from Noncontrolling Interest in Subsidiary	0	0	1,301
Fair Value of Assets Acquired	26,613	46,811	0
Liabilities Assumed	$ 27,608	$ 47,197	$ 0