Assets classified as "held for sale" (Details)	3 Months Ended			6 Months Ended
	Jun. 30, 2016 USD ($) a ft² land_parcel	Mar. 31, 2016 USD ($)	Jun. 30, 2015 USD ($) property	Jun. 30, 2016 USD ($) a ft² property land_parcel	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2015 ft²
Income from assets held for sale [Abstract]
Proceeds from sale of properties				$ 16,905,000	$ 92,455,000
Real Estate Revenue, Net	$ 226,076,000		$ 204,156,000	442,165,000	400,909,000
Assets	9,144,830,000			9,144,830,000		$ 8,881,017,000
Asia
Net assets held for sale [Abstract]
Total assets	72,575,000			72,575,000		229,561,000
Total liabilities	(19,712,000)			(19,712,000)		(11,416,000)
Total accumulated other comprehensive loss	44,662,000			44,662,000		44,598,000
Net assets classified as held for sale	97,525,000			97,525,000		262,743,000
Income from assets held for sale [Abstract]
Total revenues	3,297,000		1,732,000	6,516,000	3,384,000
Operating expenses	(2,417,000)		(1,861,000)	(4,724,000)	(3,184,000)
Total revenues less operating expenses	880,000		(129,000)	1,792,000	200,000
General and administrative	(757,000)		(1,023,000)	(1,722,000)	(2,828,000)
Income (loss) from assets held for sale before depreciation and impairment	123,000		(1,152,000)	70,000	(2,628,000)
Depreciation expense	(761,000)		(2,022,000)	(3,009,000)	(4,148,000)
Impairment of real estate	(154,117,000)		0	(183,097,000)	(14,510,000)
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	$ 40,200,000			$ 40,200,000
Square Footage of Real Estate Property, Ground up Development | a	191			191
Income (loss) from assets classified as held for sale	$ (154,755,000)		(3,174,000)	$ (186,036,000)	(21,286,000)
North America
Assets held for sale [Line Items]
Number of properties | property				2
Aggregate area | ft²	90,690			90,690
Net assets held for sale [Abstract]
Total assets	$ 15,154,000			$ 15,154,000		12,896,000
Total liabilities	0			0		0
Net assets classified as held for sale	15,154,000			15,154,000		$ 12,896,000
Income from assets held for sale [Abstract]
Total revenues	648,000		1,152,000	1,650,000	2,152,000
Operating expenses	(200,000)		(574,000)	(569,000)	(1,144,000)
Total revenues less operating expenses	448,000		578,000	1,081,000	1,008,000
General and administrative	(29,000)		(14,000)	(31,000)	(16,000)
Depreciation expense	(7,000)		(443,000)	(122,000)	(787,000)
Impairment of real estate	(863,000)		0	(863,000)	0
Income (loss) from assets classified as held for sale	$ (451,000)		$ 121,000	$ 65,000	$ 205,000
North America | Assets held for sale sold in 2015
Assets held for sale [Line Items]
Aggregate area | ft²							153,874
Income from assets held for sale [Abstract]
Number of properties sold | property			2
China and India
Assets held for sale [Line Items]
Number of properties | property				8
Aggregate area | ft²	1,200,000			1,200,000
INDIA | Parcels Aggregating 28 Acres
Assets held for sale [Line Items]
Number of properties | land_parcel	1			2
Aggregate area | a	28			28
Income from assets held for sale [Abstract]
Impairment of real estate		$ (29,000,000)
Disposal Group, Including Assets Held for Sale Not Qualifying as Discontinued Operations, Selling Costs		10,200,000
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax		$ 10,600,000
Square Footage of Real Estate Property, Ground up Development | a	5			5
Sales of Real Estate	$ 7,500,000
Gains (Losses) on Sales of Investment Real Estate	$ 0
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | Asia
Income from assets held for sale [Abstract]
Concentration Risk, Percentage		1.50%
Geographic Concentration Risk [Member] | Assets, Total [Member] | Asia
Income from assets held for sale [Abstract]
Concentration Risk, Percentage		2.50%