Dispositions (Real Estate Assets Held for Sale) (Details) $ in Thousands	Dec. 31, 2016 USD ($) property parcel	Dec. 31, 2015 USD ($) property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of Properties Held for Sale | property	7	11
Assets Held for Sale	$ 54,961	$ 93,060
Liabilities Held for Sale	$ 1,462	$ 34,340
Triple-net leased properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of Properties Held for Sale | property	0	2
Assets Held for Sale	$ 0	$ 4,488
Liabilities Held for Sale	$ 0	$ 44
Office operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of Properties Held for Sale | property	7	8
Assets Held for Sale	$ 53,151	$ 68,619
Liabilities Held for Sale	$ 1,462	$ 24,759
Seniors living operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of Properties Held for Sale | property	0	1
Assets Held for Sale	$ 1,810	$ 19,953
Liabilities Held for Sale	$ 0	$ 9,537
Number of land parcel classified as held for sale | parcel	1