Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net income	$ 38,901	$ 36,495	$ 34,449
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	23,843	23,751	24,110
Gain from disposal of properties classified as discontinued operations	(3,891)	(6,199)
Realized and unrealized gain from restricted investment		4,067	5,011
Dividend income from restricted investment			(726)
Equity in earnings of unconsolidated joint venture	27	303	309
Distributions from unconsolidated joint venture	300	300	250
Interest earned on restricted cash		(12)	(94)
Lease termination fee income related to restricted cash	10,865	10,381	10,864
Stock-based compensation	57	160	352
Other		9
Change in operating assets and liabilities:
Proceeds from restricted investment		16,211	3,646
Deferred rent	1,291	770	(870)
Other assets	2,068	(2,158)	(4,700)
Interest payable	(53)	86	68
Security deposits	(288)	(244)	(423)
Prepaid rent	(690)	(13)	2,575
Accounts payable and accrued expenses	105	6,601	(8,109)
Net cash provided by operating activities	72,481	81,768	56,072
Cash flows from investing activities:
Improvements to investments in real estate	(2,442)	(2,841)	(178)
Purchase of office equipment		(39)
Net proceeds from sale of properties	3,497	6,686
Acquisition of properties	(10,825)	(3,853)
Decrease (increase) in restricted cash	6,803	(6,691)	(100)
Proceeds received from note receivable	7,123
Net cash provided by (used in) investing activities	4,156	(6,738)	(278)
Cash flows from financing activities:
Proceeds from mortgage loan payable		40,000
Principal payments on mortgage notes payable	(14,604)	(13,048)	(12,090)
Principal payments on mortgage notes payable (related parties)	(582)	(540)	(500)
Proceeds from note payable (related parties)	18,852	53,025	39,420
Payment on note payable (related parties)	(18,852)	(62,350)	(39,420)
Proceeds from note payable			22,000
Payment on note payable	(10,776)	(10,381)
Net borrowings (repayments) on revolving line of credit	3,305	(14,466)	1,387
Debt issuance costs	(21)	(457)
Net proceeds from exercise of stock options		67
Distributions paid to noncontrolling interests	(45,846)	(50,709)	(50,775)
Dividends paid to common stockholders	(12,101)	(13,169)	(14,830)
Net cash used in financing activities	(80,625)	(72,028)	(54,808)
Net (decrease) increase in cash and cash equivalents	(3,988)	3,002	986
Cash and cash equivalents, beginning of year	3,988	986
Cash and cash equivalents, end of year		$ 3,988	$ 986