Equity Investees (Schedule of Balance Sheet Information for Equity Investees) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Current assets	$ 34,381	$ 35,375
Fixed assets, net	362,214	365,563
Other assets	14,927	3,177
Total assets	411,522	404,115
Liabilities and equity
Current liabilities	23,289	23,928
Other liabilities	249,610	230,327
Equity	138,623	149,860
Total liabilities and equity	$ 411,522	$ 404,115