Dispositions and Real Estate Assets Held for Sale - Operating Properties Held for Sale - Major Classes of Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	$ 9,417	$ 117,666
Land and land improvements [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	2,693	10,534
Building and building improvements [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	10,500	144,716
Undeveloped land [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	0	4,824
Total real estate held for sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	13,193	160,074
Accumulated depreciation and amortization [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	3,900	46,191
Total real estate held for sale, net [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	9,293	113,883
Deferred rent receivables, net [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	0	2,500
Deferred leasing costs [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	0	1,115
Prepaid expenses and other current assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	124	168
Secured debt [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	0	561
Accounts payable and accrued liabilities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	56	2,497
Deferred lease revenue [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	0	2,899
Rents received in advance and tenant security deposits [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	0	1,586
Liabilities and deferred revenue of real estate assets held for sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate held-for-sale	$ 56	$ 7,543