Equity Investments (Details 3) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Income Statements:
Rental income	$ 251,246	$ 210,673
Operating expenses	(104,090)	(90,397)
Acquisition related costs	(2,502)	(2,559)
General and administrative	(12,310)	(10,959)
Operating income	70,993	54,469
Interest and other income	288	708
Interest expense	(49,106)	(47,414)
Equity in Earnings (Loss)	2,958	2,712
Income before income tax expense	25,066	10,475
Income tax expense	(492)	(346)
Net income	24,574	46,612
Weighted average common shares outstanding	83,722	72,139
GOV
Income Statements:
Rental income	50,455	39,228
Operating expenses	(18,221)	(14,885)
Depreciation and amortization	(12,072)	(8,386)
Acquisition related costs	(49)	(829)
General and administrative	(3,039)	(2,343)
Operating income	17,074	12,785
Interest and other income	8	15
Interest expense	(4,023)	(2,537)
Equity in Earnings (Loss)	2,913	37
Income before income tax expense	13,104	10,300
Income tax expense	(45)	(46)
Net income	$ 13,059	$ 10,254
Weighted average common shares outstanding	47,052	40,501
Net income per common share (in dollars per share)	$ 0.28	$ 0.25
AIC
Income Statements:
Number of other companies which are shareholders of related party	5