Equity Investees (Schedule of Operations for Equity Investees) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Equity Method Investments and Joint Ventures [Abstract]
Revenues	$ 30,597	$ 31,219	$ 88,003	$ 90,658
Operating income	22,334	23,107	63,159	68,166
Net income	$ 20,739	$ 21,921	$ 58,754	$ 64,670