Consolidated Statements Of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 154,333,000	$ 159,365,000	$ 152,716,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	71,349,000	67,173,000	59,525,000
Amortization	4,437,000	5,790,000	3,563,000
Straight-line rental income	(22,787,000)	(26,090,000)	(22,198,000)
Non-cash interest income on construction loan	(1,680,000)	(792,000)	(1,021,000)
Loan and realty losses (recoveries), net	(5,115,000)	0	(15,856,000)
Gain on sale of real estate	0	(50,000)	(4,582,000)
Loss on extinguishment of debt	(738,000)	(2,214,000)	0
Gain on purchase liability settlement	0	0	1,657,000
Net realized gains on sales of marketable securities	0	(10,038,000)	(29,673,000)
Share-based compensation	2,490,000	2,612,000	1,732,000
Amortization of commitment fees and note receivable discounts	(662,000)	(517,000)	(693,000)
Payment of lease incentives	(5,280,000)	0	0
Amortization of Lease Incentives	387,000	119,000	40,000
Income from equity-method investee	0	0	1,214,000
Change in operating assets and liabilities:
Equity-method investment and other assets	(5,298,000)	(3,602,000)	437,000
Accounts payable and accrued expenses	4,587,000	1,607,000	2,764,000
Deferred income	140,000	304,000	(1,385,000)
Net cash provided by operating activities	207,869,000	198,095,000	176,638,000
Cash flows from investing activities:
Investment in mortgage and other notes receivable	(106,991,000)	(49,853,000)	(92,051,000)
Collection of mortgage and other notes receivable	4,346,000	43,168,000	84,228,000
Investment in real estate	(131,758,000)	(157,214,000)	(359,257,000)
Investment in real estate development	0	(10,691,000)	(32,102,000)
Investment in renovations of existing real estate	(15,887,000)	(7,888,000)	(3,378,000)
Payment allocated to cancellation of lease purchase option	0	0	6,400,000
Payment of real estate purchase liability	0	0	(8,208,000)
Proceeds from disposition of real estate properties	0	450,000	27,723,000
Proceeds from sales of marketable securities	0	18,182,000	59,607,000
Net cash used in investing activities	250,290,000	163,846,000	329,838,000
Cash flows from financing activities:
Payments on revolving credit facility	306,000,000	269,000,000	124,000,000
Payments on revolving credit facility	(443,000,000)	(206,000,000)	0
Borrowings on term loan	300,000,000	250,000,000	75,000,000
Payments of term loans	(1,144,000)	(250,822,000)	(767,000)
Debt issuance costs	(2,171,000)	(4,935,000)	(258,000)
Taxes remitted in relation to employee stock options exercised	(1,835,000)	(571,000)	(1,133,000)
Proceeds from equity offering, net	81,784,000	122,237,000	104,190,000
Convertible bond redemption	(29,985,000)	(60,921,000)	0
Proceeds from exercise of stock options	0	0	(1,000)
Distributions to noncontrolling interest	0	0	(1,565,000)
Distribution to acquire non-controlling interest	0	0	(17,000,000)
Dividends paid to stockholders	(165,391,000)	(153,040,000)	(138,303,000)
Net cash provided by (used in) financing activities	44,258,000	(35,052,000)	144,165,000
Increase (decrease) in cash and cash equivalents	1,837,000	(803,000)	(9,035,000)
Cash and cash equivalents and restricted cash, beginning of period	8,075,000	8,878,000	17,913,000
Cash and cash equivalents and restricted cash, end of period	9,912,000	8,075,000	8,878,000
Supplemental disclosure of cash flow information:
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	45,882,000	43,191,000	39,539,000
Supplemental schedule of non-cash investing and financing activities:
Settlement of mortgage note by real estate acquisition	1,800,000	0	0
Tax deferred exchange funds applied to investment in real estate	0	0	(227,000)
Conditional consideration in asset acquisition	(750,000)	0	0
Settlement of contingent asset acquisition liability	818,000	0	0
Accounts payable increase due to investments in real estate	(1,689,000)	(1,855,000)	(430,000)
Tenant investment in leased asset	3,775,000	1,250,000	0
Reclass of note balance into real estate investment	0	0	9,753,000
Assumption of debt in real estate acquisition	0	18,311,000	0
Unsettled marketable securities sales transactions	0	0	6,464,000
Non-cash sale of equity-method investment	0	0	8,100,000
Tenant forfeiture of lease escrow deposit	$ 10,637,000	$ 0	$ 0