Equity Investments (Details3) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended						1 Months Ended	12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 GOV	Dec. 31, 2010 GOV	Dec. 31, 2009 GOV	Jun. 30, 2011 AIC Y	Dec. 31, 2011 AIC Y company
Income Statements:
Rental income	$ 241,552	$ 241,785	$ 217,938	$ 210,673	$ 200,645	$ 196,272	$ 192,930	$ 192,616	$ 911,948	$ 782,463	$ 764,461	$ 178,950	$ 117,219	$ 79,161
Operating expenses									(392,131)	(333,049)	(324,050)	(66,445)	(41,178)	(27,307)
Depreciation and amortization												(40,089)	(24,239)	(15,172)
Acquisition related costs									(10,073)	(21,553)	(4,082)	(3,504)	(5,750)	(1,032)
General and administrative									(46,758)	(39,737)	(36,603)	(10,898)	(7,061)	(4,058)
Operating income									233,943	53,179	206,513	58,014	38,991	31,592
Interest and other income												104	103	53
Interest expense									(195,024)	(179,642)	(166,855)	(12,057)	(7,351)	(5,556)
Loss on extinguishment of debt									(35)	(796)	20,686		(3,786)
Equity in Earnings (Loss)									11,377	8,464	6,546	139	(1)	(15)
Income before income tax expense									63,156	(60,596)	68,085	46,200	27,956	26,074
Income tax expense									(1,347)	(550)	(735)	(203)	(161)	(93)
Net income available for common shareholders	$ 1,050	$ 14,712	$ 9,464	$ 37,773	$ 6,651	$ 53,143	$ (2,669)	$ 24,630	$ 62,999	$ 81,755	$ 114,006	$ 45,997	$ 27,795	$ 25,981
Weighted average common shares outstanding									77,428	64,703	56,055	43,368	34,341	15,082
Net income per common share (in dollars per share)												$ 1.06	$ 0.81	$ 1.72
Number of other companies which are shareholders of related party																5
Period for which property insurance program was extended (in years)															1	1