Supplemental Cash Flow Information (Narrative) (Details) - USD ($) $ in Thousands		12 Months Ended
	Nov. 03, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Significant Noncash Transactions [Line Items]
Liabilities assumed	$ 17,613
Assets contributed	$ 32,893
Capital Lease Obligations
Other Significant Noncash Transactions [Line Items]
Non-cash capital lease arrangements			$ 55	$ 732
Notes Received from Property Sales
Other Significant Noncash Transactions [Line Items]
Purchased goods and services		$ 27,358	$ 2,355	$ 11,962