Consolidated Statements Of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Cash Flows [Abstract]
Tax deferred exchange funds applied to investment in real estate	$ 0	$ 0	$ 23,813,000
Cash flows from operating activities:
Net income	152,716,000	150,314,000	103,052,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	59,565,000	53,163,000	38,078,000
Amortization	3,563,000	3,472,000	2,611,000
Amortization of commitment fees and note receivable discounts	(693,000)	0	0
Straight-line rental income	(22,198,000)	(24,623,000)	(16,463,000)
Non-cash interest income on construction loan	(1,021,000)	(411,000)	0
Unamortized debt premium written off	0	0	(1,655,000)
Write-off of debt issuance costs	0	0	2,145,000
Loan and realty losses (recoveries), net	(15,856,000)	491,000	0
Gain on sale of real estate	(4,582,000)	(1,126,000)	0
Gain on sale of equity-method investee	1,657,000	0	0
Net realized gains on sales of marketable securities	(29,673,000)	(23,529,000)	0
Share-based compensation	1,732,000	2,134,000	2,020,000
Income from equity-method investee	1,214,000	1,767,000	71,000
Change in operating assets and liabilities:
Equity-method investment and other assets	1,018,000	216,000	(2,334,000)
Accounts payable and accrued expenses	2,764,000	1,038,000	1,448,000
Deferred income	(1,385,000)	2,501,000	(2,830,000)
Net cash provided by operating activities	177,219,000	164,425,000	126,143,000
Cash flows from investing activities:
Investment in mortgage and other notes receivable	(92,051,000)	(92,249,000)	(4,447,000)
Collection of mortgage and other notes receivable	84,228,000	21,495,000	1,456,000
Investment in real estate	(359,257,000)	(106,315,000)	(520,505,000)
Investment in real estate development	(32,102,000)	(14,641,000)	(8,455,000)
Investment in renovations of existing real estate	(3,378,000)	(3,157,000)	(4,211,000)
Payments into facility repair escrows	0	0	(1,554,000)
Payment of real estate purchase liability	0	0	(2,600,000)
Payment allocated to cancellation of lease purchase option	(6,400,000)	0	0
Long-term escrow deposit	(8,208,000)	0	0
Proceeds from disposition of real estate properties	27,723,000	9,593,000	0
Purchases of marketable securities	0	(8,458,000)	0
Proceeds from sales of marketable securities	59,607,000	57,406,000	0
Net cash used in investing activities	329,838,000	136,326,000	540,316,000
Cash flows from financing activities:
Net change in borrowings under revolving credit facilities	124,000,000	(340,000,000)	207,000,000
Proceeds from convertible senior notes	0	0	200,000,000
Proceeds from issuance of secured debt	0	78,084,000	38,007,000
Borrowings on term loan	75,000,000	325,000,000	130,000,000
Payments of term loans	(767,000)	(742,000)	(328,515,000)
Debt issuance costs	(258,000)	(2,608,000)	(8,443,000)
Taxes remitted in relation to employee stock options exercised	(1,133,000)	0	0
Proceeds from equity offering, net	104,190,000	49,114,000	270,798,000
Proceeds from exercise of stock options	(1,000)	(1,000)	0
Distributions to noncontrolling interest	(1,565,000)	(2,292,000)	(2,049,000)
Distribution to acquire non-controlling interest	(17,000,000)	0	0
Dividends paid to stockholders	(138,303,000)	(124,657,000)	(100,650,000)
Net cash provided by (used in) financing activities	144,165,000	(18,100,000)	406,148,000
(Decrease) increase in cash and cash equivalents	(8,454,000)	9,999,000	(8,025,000)
Cash and cash equivalents, beginning of year	13,286,000	3,287,000	11,312,000
Cash and cash equivalents, end of year	4,832,000	13,286,000	3,287,000
Supplemental disclosure of cash flow information:
Interest Paid	39,539,000	31,289,000	22,172,000
Supplemental schedule of non-cash investing and financing activities:
Tax deferred exchange funds applied to investment in real estate	(227,000)	0	0
Conditional consideration in asset acquisition	0	(3,000,000)	0
Settlement of contingent asset acquisition liability	0	750,000	3,000,000
Accounts payable increase due to investments in real estate	(430,000)	(1,076,000)	(2,091,000)
Accounts payable increase due to escrow deposits	0	0	2,062,000
Reclass of note balance into real estate investment	9,753,000	255,000	0
Assumption of debt in real estate acquisition	0	0	7,858,000
Unsettled marketable securities sales transactions	6,464,000	0	0
Conversion of equity-method investment	8,100,000	0	0
Assignment of net assets in equity-method investee	(1,506,000)	(6,062,000)	(10,304,000)
Conversion of investment in preferred stock to common	$ 0	$ 38,132,000	$ 0