Equity Investments (Details 3) (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Income Statements:
Rental income	$ 238,790	$ 193,059	$ 662,596	$ 572,205
Operating expenses	(100,912)	(83,023)	(275,760)	(240,280)
Depreciation and amortization	(56,389)	(42,794)	(159,072)	(130,560)
Acquisition related costs	(4,805)	(1,559)	(9,722)	(2,965)
General and administrative	(11,450)	(9,704)	(33,559)	(28,081)
Operating income	65,234	55,979	184,483	148,828
Interest and other income	369	571	1,428	2,134
Interest expense	(49,423)	(44,192)	(145,037)	(133,716)
Equity in earnings (losses) of an investee	2,768	1,999	8,390	6,643
Income before income tax expense	30,435	31,951	60,751	57,901
Income tax benefit (expense)	(307)	34	(743)	(329)
Net income	28,535	65,810	95,111	113,105
Weighted average common shares outstanding (in shares)	81,536	65,173	75,307	62,198
GOV
Income Statements:
Rental income	45,719	30,746	126,718	80,040
Operating expenses	(16,951)	(11,275)	(46,937)	(27,537)
Depreciation and amortization	(10,379)	(6,321)	(27,862)	(16,602)
Acquisition related costs	(1,008)	(2,687)	(2,846)	(4,542)
General and administrative	(2,746)	(1,833)	(7,655)	(4,915)
Operating income	14,635	8,630	41,418	26,444
Interest and other income	54	12	89	80
Interest expense	(3,162)	(1,973)	(8,775)	(5,182)
Equity in earnings (losses) of an investee	28	35	111	(17)
Income before income tax expense	11,555	6,704	32,843	21,325
Income tax benefit (expense)	8	(35)	(94)	(71)
Net income	$ 11,563	$ 6,669	$ 32,749	$ 21,254
Weighted average common shares outstanding (in shares)	45,322	36,369	42,127	32,265
Net income per common share (in dollars per share)	$ 0.26	$ 0.18	$ 0.78	$ 0.66