Additional Balance Sheet Detail and 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]
Other Significant Noncash Transaction, Value of Consideration Given	$ 34,604	$ 32,243	$ 4,123
Extinguishment of Debt, Amount	0	10,616	53,373
Noncash or Part Noncash Acquisition, Other Assets Acquired	131,833	0	297,821
Interest Paid	21,943	41,919	41,442
Income Taxes Paid	$ 13,000	$ 17,181	$ 1,937