Taxable Income (Details) (USD $) In Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Taxable Income
Net income (loss) attributable to common stockholders	$ 2,011		$ 6,474		$ (3,778)		$ 11,068
Reconciling items to taxable income:
Depreciation and amortization	4,194		5,088		9,519		10,140
Gain or loss on disposition of depreciable assets	78		809		(2,098)		7,084
Straight-line rent	(1,009)		(631)		(2,149)		(1,112)
Receivable allowances	324		61		720		(594)
Stock-based compensation	1,298		184		2,684		1,359
Other	5,955		(1,787)		7,044		(1,062)
Taxable income (loss)	12,851	[1]	10,198	[1]	11,942	[1]	26,883	[1]
Dividends paid	22,325		18,953		42,570		37,370
State Income Tax Expense [Abstract]
Texas gross margin tax	108		117		227		228
State Income Tax Expense Other	(126)		48		(83)		96
Total state income tax expense	(18)		165		144		324
State income tax payments, net of refunds	$ 481		$ 497		$ 503		$ 491

[1] Before REIT dividend paid deduction.