Equity Investees (Schedule of Operations for Equity Investees) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity Method Investments and Joint Ventures [Abstract]
Revenues	$ 191,078	$ 193,038	$ 189,941
Operating Income	139,604	122,836	12,191
Net Income	$ 134,479	$ 118,175	$ 7,810