Property Dispositions - Narratives (Details) $ in Thousands			3 Months Ended						12 Months Ended
	Mar. 17, 2017 USD ($) property	Mar. 13, 2017 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($) property	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) property	Dec. 31, 2015 USD ($)	Dec. 31, 2012 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Financing receivable			$ 619,728		$ 539,892				$ 619,728	$ 539,892
Impairment charges						$ 29,200
Payments of mortgage principal									458,010	177,469	$ 121,267
Loss on extinguishment of debt					$ (800)	$ (16,000)	$ (5,100)	$ (2,500)	(1,922)	$ (24,376)	(275)
Property in Italy
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments of mortgage principal									9,300
I Drive Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Financing receivable	$ 34,000
Deferred gain on the sale of property	2,100
Loss on extinguishment of debt									(1,300)
I Drive Property | Developer
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Non recourse mortgage loan paid by buyer	60,000		60,000						60,000
I Drive Wheel
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Financing receivable												$ 50,000
Deferred gain on the sale of property	$ 16,400
Self storage
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | property										34
Nonrecurring | Level 3
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charges									19,535	$ 31,625	1,023
Nonrecurring | Level 3 | Real estate
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charges			4,200						8,276	$ 29,183	0
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sales of real estate		$ 14,100
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Property in Italy
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | property				3
Proceeds from sales of real estate				$ 14,600
Gain on sale of real estate, net of tax				$ 1,200
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | property										34
Gain on sale of real estate, net of tax		$ 1,600							2,879	$ 132,858	$ 2,197
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | KBR
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accelerated amortization of intangible liability									3,300	$ 13,900
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | I Drive Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | property	1
Proceeds from sales of real estate	$ 23,500
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Self storage
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | property										34
Proceeds from sales of real estate										$ 259,100
Gain on sale of real estate, net of tax										132,900
Payments of mortgage principal										84,700
Loss on extinguishment of debt										$ (15,800)
Discontinued Operations, Disposed of by Means Other than Sale | KBR
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Intangible liability			$ 15,700						$ 15,700