Consolidated Statements Of Cash Flows (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income	$ 90,898,000	$ 81,132,000	$ 69,421,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	16,981,000	11,992,000	11,203,000
Straight-line rental income	(3,664,000)	(3,778,000)	(3,140,000)
Non-cash interest income on construction loan	0	(1,082,000)	(298,000)
Loan and realty losses (recoveries)	2,195,000	99,000	573,000
Gain on sales of real estate	(11,966,000)	(3,348,000)	(2,004,000)
Gain on payoff of mortgage note	(4,605,000)	0	0
Net realized gains on sales of marketable securities	(30,000)	(9,899,000)	0
Share-based compensation	2,168,000	3,087,000	2,368,000
Change in fair value of interest rate swap agreement	0	1,197,000	0
Income from unconsolidated entity	(45,000)	0	0
Change in operating assets and liabilities:
Deferred costs and other assets	(425,000)	(2,655,000)	(643,000)
Accounts payable and accrued expenses	(512,000)	95,000	634,000
Deferred income	(339,000)	212,000	576,000
Net cash provided by operating activities	86,266,000	76,854,000	77,544,000
Cash flows from investing activities:
Investment in mortgage notes receivable	(16,241,000)	(6,566,000)	(12,422,000)
Collection of mortgage notes receivable	17,463,000	4,540,000	9,482,000
Investment in real estate properties	(110,601,000)	(75,806,000)	(98,736,000)
Investment in unconsolidated subsidiary	(8,309,000)	0	0
Payment of real estate purchase liability	(5,222,000)	0	0
Receipt of earnest money deposit	0	525,000	3,325,000
Proceeds from disposition of real estate properties	22,975,000	8,971,000	6,247,000
Proceeds from sales of marketable securities	125,000	12,862,000	75,000
Net cash used in investing activities	(99,810,000)	(55,474,000)	(92,029,000)
Cash flows from financing activities:
Net change in borrowings under a revolving credit facility	(33,300,000)	59,535,000	37,765,000
Borrowings on term loan	120,000,000	50,000,000	0
Debt issuance costs	(766,000)	0	0
Principal payments on debt	0	(50,000,000)	0
Stock options exercised	2,000	(200,000)	(183,000)
Distributions to noncontrolling interest	(177,000)	0	0
Dividends paid to stockholders	(78,925,000)	(67,893,000)	(66,517,000)
Net cash provided by (used in) financing activities	6,830,000	(8,158,000)	(28,569,000)
(Decrease) increase in cash and cash equivalents	(6,714,000)	13,222,000	(43,054,000)
Cash and cash equivalents, beginning of year	15,886,000	2,664,000	45,718,000
Cash and cash equivalents, end of year	9,172,000	15,886,000	2,664,000
Supplemental disclosure of cash flow information:
Interest Paid	3,449,000	3,353,000	1,061,000
Supplemental schedule of non-cash investing and financing activities:
Settlement of mortgage note by real estate acquisition	0	0	22,936,000
Cash withheld at closing of real estate acquisition	0	5,478,000	1,000,000
Discount on mortgage note receivable purchased	0	204,000	0
Assumption of debt in real estate acquisition	19,250,000	0	0
Noncontrolling interest conveyed in acquisition	10,964,000	0	0
Decrease in fair value of cash flow hedge	$ (1,241,000)	$ 0	$ 0