Segment Information (Reconciliation Of Adjusted Earnings Before Interest, Taxes, Depreciation And Amortization To Net Income Attributable To Controlling Interests) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Segment Information [Abstract]
Adjusted EBITDA	$ 48,526	$ 44,484
Loss on disposal of assets	203	548
Other income	(421)	(77)
Noncontrolling interests	(419)	(410)
Stock-based compensation expense	3,157	2,551
Acquisition-related expenses	2,822	1,087
Other adjustment to selling, general, and administrative expenses	446
EBITDA	42,738	40,785
Interest expense, net, including amortization of deferred financing costs	5,295	5,585
Income tax expense	5,980	6,146
Depreciation and accretion expense	16,285	13,750
Amortization expense	5,748	5,475
Net income attributable to controlling interests and available to common stockholders	$ 9,430	$ 9,829