Schedule III - Real Estate Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	$ 52,899
Initial costs of buildings and improvements	373,326
Initial costs of construction in progress	270,123
Costs capitalized subsequent to acquisition, Land	77,706
Costs capitalized subsequent to acquisition, Buildings and improvements	1,805,575
Costs capitalized subsequent to acquisition, Construction in progress	650,799
Gross carrying amount, Land	130,605
Gross carrying amount, Buildings and improvements	2,178,901
Gross carrying amount, Construction in progress	920,922
Accumulated depreciation and amortization	(558,560)	$ (467,644)	$ (394,823)	$ (317,834)
Tax Basis of Investments, Cost for Income Tax Purposes	3,410,000
Owned Properties
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	52,899
Initial costs of buildings and improvements	312,254
Initial costs of construction in progress	270,123
Costs capitalized subsequent to acquisition, Land	77,706
Costs capitalized subsequent to acquisition, Buildings and improvements	1,782,946
Costs capitalized subsequent to acquisition, Construction in progress	650,132
Gross carrying amount, Land	130,605
Gross carrying amount, Buildings and improvements	2,095,200
Gross carrying amount, Construction in progress	920,255
Accumulated depreciation and amortization	(536,167)
Owned Properties | Atlanta, Georgia Campus
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	12,647
Initial costs of buildings and improvements	35,473
Initial costs of construction in progress	2,209
Costs capitalized subsequent to acquisition, Land	31,941
Costs capitalized subsequent to acquisition, Buildings and improvements	489,827
Costs capitalized subsequent to acquisition, Construction in progress	126,721
Gross carrying amount, Land	44,588
Gross carrying amount, Buildings and improvements	525,300
Gross carrying amount, Construction in progress	128,930
Accumulated depreciation and amortization	$ (190,566)
Date of acquisition	Oct. 03, 2006
Owned Properties | Irving, Texas
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of buildings and improvements	$ 5,808
Costs capitalized subsequent to acquisition, Land	8,606
Costs capitalized subsequent to acquisition, Buildings and improvements	363,919
Costs capitalized subsequent to acquisition, Construction in progress	98,170
Gross carrying amount, Land	8,606
Gross carrying amount, Buildings and improvements	369,727
Gross carrying amount, Construction in progress	98,170
Accumulated depreciation and amortization	$ (59,719)
Date of acquisition	Feb. 08, 2013
Owned Properties | Richmond, Virginia
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	$ 2,000
Initial costs of buildings and improvements	11,200
Initial costs of construction in progress	7,029
Costs capitalized subsequent to acquisition, Land	180
Costs capitalized subsequent to acquisition, Buildings and improvements	184,484
Costs capitalized subsequent to acquisition, Construction in progress	132,919
Gross carrying amount, Land	2,180
Gross carrying amount, Buildings and improvements	195,684
Gross carrying amount, Construction in progress	139,948
Accumulated depreciation and amortization	$ (74,056)
Date of acquisition	Mar. 20, 2010
Owned Properties | Richmond 01 Virginia
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Date of acquisition	Nov. 15, 2019
Owned Properties | Chicago, Illinois
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of construction in progress	$ 17,764
Costs capitalized subsequent to acquisition, Land	9,400
Costs capitalized subsequent to acquisition, Buildings and improvements	205,026
Costs capitalized subsequent to acquisition, Construction in progress	69,114
Gross carrying amount, Land	9,400
Gross carrying amount, Buildings and improvements	205,026
Gross carrying amount, Construction in progress	86,878
Accumulated depreciation and amortization	$ (19,760)
Date of acquisition	Jul. 08, 2014
Owned Properties | Suwanee, Georgia
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	$ 1,395
Initial costs of buildings and improvements	29,802
Costs capitalized subsequent to acquisition, Land	2,126
Costs capitalized subsequent to acquisition, Buildings and improvements	144,322
Costs capitalized subsequent to acquisition, Construction in progress	5,559
Gross carrying amount, Land	3,521
Gross carrying amount, Buildings and improvements	174,124
Gross carrying amount, Construction in progress	5,559
Accumulated depreciation and amortization	$ (78,510)
Date of acquisition	Sep. 01, 2005
Owned Properties | Piscataway New Jersey
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	$ 7,466
Initial costs of buildings and improvements	80,366
Initial costs of construction in progress	13,900
Costs capitalized subsequent to acquisition, Buildings and improvements	23,187
Costs capitalized subsequent to acquisition, Construction in progress	22,156
Gross carrying amount, Land	7,466
Gross carrying amount, Buildings and improvements	103,553
Gross carrying amount, Construction in progress	36,056
Accumulated depreciation and amortization	$ (10,634)
Date of acquisition	Jun. 06, 2016
Owned Properties | Santa Clara, California
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of buildings and improvements	$ 15,838
Costs capitalized subsequent to acquisition, Buildings and improvements	98,661
Costs capitalized subsequent to acquisition, Construction in progress	1,238
Gross carrying amount, Buildings and improvements	114,499
Gross carrying amount, Construction in progress	1,238
Accumulated depreciation and amortization	$ (46,536)
Date of acquisition	Nov. 01, 2007
Owned Properties | Sacramento, California
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	$ 1,481
Initial costs of buildings and improvements	52,753
Costs capitalized subsequent to acquisition, Buildings and improvements	12,505
Costs capitalized subsequent to acquisition, Construction in progress	163
Gross carrying amount, Land	1,481
Gross carrying amount, Buildings and improvements	65,258
Gross carrying amount, Construction in progress	163
Accumulated depreciation and amortization	$ (13,905)
Date of acquisition	Dec. 21, 2012
Owned Properties | Fort Worth, Texas
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	$ 136
Initial costs of buildings and improvements	610
Initial costs of construction in progress	48,984
Costs capitalized subsequent to acquisition, Land	8,943
Costs capitalized subsequent to acquisition, Buildings and improvements	54,408
Costs capitalized subsequent to acquisition, Construction in progress	(13,262)
Gross carrying amount, Land	9,079
Gross carrying amount, Buildings and improvements	55,018
Gross carrying amount, Construction in progress	35,722
Accumulated depreciation and amortization	$ (3,240)
Date of acquisition	Dec. 16, 2016
Owned Properties | Princeton, New Jersey
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	$ 20,700
Initial costs of buildings and improvements	32,126
Costs capitalized subsequent to acquisition, Buildings and improvements	3,066
Costs capitalized subsequent to acquisition, Construction in progress	39
Gross carrying amount, Land	20,700
Gross carrying amount, Buildings and improvements	35,192
Gross carrying amount, Construction in progress	39
Accumulated depreciation and amortization	$ (5,107)
Date of acquisition	Jun. 30, 2014
Owned Properties | Dulles, Virginia
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	$ 3,154
Initial costs of buildings and improvements	29,583
Costs capitalized subsequent to acquisition, Buildings and improvements	19,068
Costs capitalized subsequent to acquisition, Construction in progress	4,688
Gross carrying amount, Land	3,154
Gross carrying amount, Buildings and improvements	48,651
Gross carrying amount, Construction in progress	4,688
Accumulated depreciation and amortization	$ (11,831)
Date of acquisition	Oct. 06, 2017
Owned Properties | Ashburn, Virginia
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of construction in progress	$ 75,371
Costs capitalized subsequent to acquisition, Land	16,476
Costs capitalized subsequent to acquisition, Buildings and improvements	156,396
Costs capitalized subsequent to acquisition, Construction in progress	114,004
Gross carrying amount, Land	16,476
Gross carrying amount, Buildings and improvements	156,396
Gross carrying amount, Construction in progress	189,375
Accumulated depreciation and amortization	$ (7,363)
Date of acquisition	Aug. 09, 2017
Owned Properties | Ashburn Virginia 01
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Date of acquisition	Oct. 23, 2017
Owned Properties | Ashburn Virginia 02
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Date of acquisition	Jul. 22, 2019
Owned Properties | Eemshaven, Netherlands
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of construction in progress	$ 29,915
Costs capitalized subsequent to acquisition, Construction in progress	7,352
Gross carrying amount, Construction in progress	$ 37,267
Date of acquisition	Apr. 23, 2019
Owned Properties | Phoenix, Arizona
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of construction in progress	$ 24,668
Costs capitalized subsequent to acquisition, Buildings and improvements	2,412
Costs capitalized subsequent to acquisition, Construction in progress	7,172
Gross carrying amount, Buildings and improvements	2,412
Gross carrying amount, Construction in progress	31,840
Accumulated depreciation and amortization	$ (1,489)
Date of acquisition	Aug. 11, 2017
Owned Properties | Groningen, Netherlands
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	$ 1,743
Initial costs of buildings and improvements	8,640
Costs capitalized subsequent to acquisition, Land	(2)
Costs capitalized subsequent to acquisition, Buildings and improvements	445
Costs capitalized subsequent to acquisition, Construction in progress	3,028
Gross carrying amount, Land	1,741
Gross carrying amount, Buildings and improvements	9,085
Gross carrying amount, Construction in progress	3,028
Accumulated depreciation and amortization	$ (451)
Date of acquisition	Apr. 23, 2019
Owned Properties | Hillsboro, Oregon
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of construction in progress	$ 25,657
Costs capitalized subsequent to acquisition, Construction in progress	37,916
Gross carrying amount, Construction in progress	$ 63,573
Date of acquisition	Oct. 03, 2017
Owned Properties | Miami, Florida
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	$ 1,777
Initial costs of buildings and improvements	6,955
Costs capitalized subsequent to acquisition, Buildings and improvements	24,486
Costs capitalized subsequent to acquisition, Construction in progress	119
Gross carrying amount, Land	1,777
Gross carrying amount, Buildings and improvements	31,441
Gross carrying amount, Construction in progress	119
Accumulated depreciation and amortization	$ (12,419)
Date of acquisition	Mar. 06, 2008
Owned Properties | Lenexa, Kansas
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of land	$ 400
Initial costs of buildings and improvements	3,100
Costs capitalized subsequent to acquisition, Land	36
Costs capitalized subsequent to acquisition, Buildings and improvements	734
Gross carrying amount, Land	436
Gross carrying amount, Buildings and improvements	3,834
Accumulated depreciation and amortization	$ (580)
Date of acquisition	Jun. 03, 2011
Owned Properties | Manassas, Virginia
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of construction in progress	$ 24,626
Costs capitalized subsequent to acquisition, Construction in progress	33,036
Gross carrying amount, Construction in progress	57,662
Accumulated depreciation and amortization	(1)
Leased Properties
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of buildings and improvements	61,072
Costs capitalized subsequent to acquisition, Buildings and improvements	22,629
Costs capitalized subsequent to acquisition, Construction in progress	667
Gross carrying amount, Buildings and improvements	83,700
Gross carrying amount, Construction in progress	667
Accumulated depreciation and amortization	(22,393)
Leased Properties | Jersey City, New Jersey
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of buildings and improvements	1,985
Costs capitalized subsequent to acquisition, Buildings and improvements	28,425
Costs capitalized subsequent to acquisition, Construction in progress	557
Gross carrying amount, Buildings and improvements	30,410
Gross carrying amount, Construction in progress	557
Accumulated depreciation and amortization	$ (13,938)
Date of acquisition	Nov. 01, 2006
Leased Properties | Overland Park, Kansas
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Costs capitalized subsequent to acquisition, Buildings and improvements	$ 888
Costs capitalized subsequent to acquisition, Construction in progress	1
Gross carrying amount, Buildings and improvements	888
Gross carrying amount, Construction in progress	1
Accumulated depreciation and amortization	(658)
Lease Facilities acquired in 2015
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial costs of buildings and improvements	59,087
Costs capitalized subsequent to acquisition, Buildings and improvements	(6,684)
Costs capitalized subsequent to acquisition, Construction in progress	109
Gross carrying amount, Buildings and improvements	52,403
Gross carrying amount, Construction in progress	109
Accumulated depreciation and amortization	$ (7,797)
Date of acquisition	Jun. 16, 2015