Business Segment Information (Reconciliation Of Segment Margin To (Loss) Income Before Income Taxes) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Segment Reporting [Abstract]
Segment margin	$ 65,929	[1]	$ 52,931	[1]	$ 189,012	[1]	$ 149,759	[1]
Corporate general and administrative expenses	(9,428)		(8,194)		(26,756)		(23,267)
Depreciation and amortization	(14,838)		(14,706)		(45,447)		(43,100)
Interest expense	(9,873)		(8,960)		(30,697)		(26,670)
Distributable cash from equity investees in excess of equity in earnings	(5,613)		(3,701)		(19,098)		(11,925)
Non-cash items not included in segment margin	(2,222)		3,061		(2,475)		2,729
Cash payments from direct financing leases in excess of earnings	(1,278)		(1,171)		(3,748)		(3,424)
Income before income taxes	$ 22,677		$ 19,260		$ 60,791		$ 44,102

[1] A reconciliation of Segment Margin to income before income taxes for the periods presented is as follows: Three Months EndedSeptember 30, Nine Months EndedSeptember 30, 2012 2011 2012 2011Segment Margin$65,929 $52,931 $189,012 $149,759Corporate general and administrative expenses(9,428) (8,194) (26,756) (23,267)Depreciation and amortization(14,838) (14,706) (45,447) (43,100)Interest expense(9,873) (8,960) (30,697) (26,670)Distributable cash from equity investees in excess of equity in earnings(5,613) (3,701) (19,098) (11,925)Non-cash items not included in segment margin(2,222) 3,061 (2,475) 2,729Cash payments from direct financing leases in excess of earnings(1,278) (1,171) (3,748) (3,424)Income before income taxes$22,677 $19,260 $60,791 $44,102