CONSOLIDATED BALANCE SHEETS - Unaudited		3 Months Ended
		Mar. 31, 2019 USD ($) ft²	Dec. 31, 2018 USD ($) ft²
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Document Period End Date		Mar. 31, 2019
ASSETS
Real estate properties		$ 2,609,914,000	$ 2,553,481,000
Development and value-add properties	[1]	264,526,000	263,664,000
Real estate, development and value-add properties		2,874,440,000	2,817,145,000
Less accumulated depreciation		(832,925,000)	(814,915,000)
Real estate, net		2,041,515,000	2,002,230,000
Unconsolidated investment		7,879,000	7,870,000
Cash		1,831,000	374,000
Other Assets		120,421,000	121,231,000
TOTAL ASSETS		2,171,646,000	2,131,705,000
LIABILITIES
Unsecured bank credit facilities		131,189,000	193,926,000
Unsecured debt		803,397,000	723,400,000
Secured debt		185,606,000	188,461,000
Accounts payable and accrued expenses		83,364,000	86,563,000
Other liabilities		46,616,000	34,652,000
Total Liabilities		1,250,172,000	1,227,002,000
Stockholders' Equity:
Common shares; $.0001 par value; 70,000,000 shares authorized; 36,752,260 shares issued and outstanding at March 31, 2019 and 36,501,356 at December 31, 2018		4,000	4,000
Excess shares; $.0001 par value; 30,000,000 shares authorized; no shares issued		0	0
Additional paid-in capital		1,245,660,000	1,222,547,000
Distributions in excess of earnings		(330,184,000)	(326,193,000)
Accumulated Other Comprehensive Income		4,388,000	6,701,000
Total Stockholders' Equity		919,868,000	903,059,000
Noncontrolling interest in joint ventures		1,606,000	1,644,000
Total Equity		921,474,000	904,703,000
TOTAL LIABILITIES AND EQUITY		$ 2,171,646,000	$ 2,131,705,000
2019 Operating Property Sales [Member] [Domain]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Footage of Real Estate Property | ft²		51,000
2018 Operating Property Sales [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Footage of Real Estate Property | ft²			339,000

[1] Value-add properties are defined as properties that are either acquired but not stabilized or can be converted to a higher and better use.  Acquired properties meeting either of the following two conditions are considered value-add properties:  (1) Less than 75% occupied as of the acquisition date (or will be less than 75% occupied within one year of acquisition date based on near term lease roll), or (2) 20% or greater of the acquisition cost will be spent to redevelop the property.