Real Estate Properties - Summary of Properties Sold (Footnote) (Details) $ in Thousands	1 Months Ended			3 Months Ended				9 Months Ended
	May. 31, 2015 building	Mar. 31, 2015 building	Jan. 31, 2013 building	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($) building	May. 31, 2015 building	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) building	Sep. 30, 2014 USD ($)
Real Estate Properties [Line Items]
Number of buildings sold			18
(Loss) gain on early extinguishment of debt | $				$ (3,887)			$ 6,699	$ 6,111	$ 6,699
Amounts reclassified from cumulative other comprehensive loss to net income | $				(1,239)				(63,825)
Foreign Currency Translation Adjustments
Real Estate Properties [Line Items]
Amounts reclassified from cumulative other comprehensive loss to net income | $				0				$ (63,207)
Disposed of by Sale
Real Estate Properties [Line Items]
Number of buildings sold								117
333 Laurel Oak Drive
Real Estate Properties [Line Items]
Number of buildings sold						3
333 Laurel Oak Drive | Disposed of by Sale
Real Estate Properties [Line Items]
Number of buildings sold	2	1
1000 Vorhees Drive and 400 Laurel Oak Drive
Real Estate Properties [Line Items]
Number of buildings sold						3
1000 Vorhees Drive and 400 Laurel Oak Drive | Disposed of by Sale
Real Estate Properties [Line Items]
Number of buildings sold	2	1
225 Water Street in Jacksonville, Florida | Mortgage notes
Real Estate Properties [Line Items]
Principal balance | $				$ 40,100				$ 40,100
(Loss) gain on early extinguishment of debt | $								$ 17,300
Australia Portfolio | Foreign Currency Translation Adjustments
Real Estate Properties [Line Items]
Amounts reclassified from cumulative other comprehensive loss to net income | $					$ 63,200
Australia Portfolio | Disposed of by Sale
Real Estate Properties [Line Items]
Number of buildings sold					11