Equity Investments (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Summarized combined financial information of entities in which Company owns equity interest
Revenues	$ 353,148	$ 347,591	$ 1,099,187	$ 1,063,656
Operating costs and expenses	321,907	314,965	974,659	960,943
Income from continuing operations before taxes	$ 31,211	$ 32,581	$ 124,447	$ 102,626