Real Estate and Other Assets Held For Sale and Discontinued Operations (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets, held for sale [Abstract]
Land	$ 0				$ 870	$ 0
Building and tenant improvements	0				21,318	0
Land held for development	0				355	0
Less accumulated depreciation	0				(9,304)	0
Net real estate assets	0				13,239	0
Accrued straight-line rents receivable, net	0				591	0
Deferred leasing costs, net	0				253	0
Prepaid expenses and other assets, net	0				35	0
Real estate and other assets, net, held for sale	0				14,118	0
Discontinued Operations [Abstract]
Rental and other revenues					0	8,484	$ 50,935
Operating expenses:
Rental property and other expenses					0	3,334	20,805
Depreciation and amortization					0	0	14,039
General and administrative					0	1,388	2,366
Total operating expenses					0	4,722	37,210
Interest expense					0	85	621
Other income					0	420	2,635
Income from discontinued operations					0	4,097	15,739
Net gains on disposition of discontinued operations					0	414,496	0
Total income from discontinued operations	$ 0	$ 0	$ 0	$ 418,593	0	418,593	15,739
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Cash flows from operating activities					0	2,040	27,579
Cash flows from investing activities					$ 0	$ 417,097	$ (16,445)