Real Estate Properties - Summary of Properties Sold (Footnote) (Details) $ in Thousands	1 Months Ended			3 Months Ended		6 Months Ended
	May. 31, 2015 building	Mar. 31, 2015 building	Jan. 31, 2013 building	Jun. 30, 2015 USD ($) building	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) building	Jun. 30, 2014 USD ($)
Real Estate Properties [Line Items]
Number of buildings sold			18
Gain on early extinguishment of debt | $				$ 10,426	$ 0	$ 9,998	$ 0
Amounts reclassified from cumulative other comprehensive loss to net income | $				64,439		62,586
Foreign Currency Translation Adjustments
Real Estate Properties [Line Items]
Amounts reclassified from cumulative other comprehensive loss to net income | $				$ 63,207		$ 63,207
Disposed of by Sale
Real Estate Properties [Line Items]
Number of buildings sold				83
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
Gain on early extinguishment of debt | $				$ 17,300		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