Real Estate Assets and Construction in Progress (Summary of Properties Owned or Leased by the Company) (Details) $ in Thousands	Dec. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($) property
Real Estate Properties [Line Items]
Land	$ 105,541	$ 88,216
Buildings, Improvements and Equipment	1,917,251	1,701,287
Construction in progress	790,064	567,819
Total cost	2,812,856	2,357,322
Manassas, Virginia
Real Estate Properties [Line Items]
Construction in progress	116,200
Manassas, Virginia | Assets Held For Sale
Real Estate Properties [Line Items]
Construction in progress	71,000
Owned Properties | Atlanta, Georgia (Atlanta-Metro)
Real Estate Properties [Line Items]
Land	20,416	20,416
Buildings, Improvements and Equipment	493,446	452,836
Construction in progress	88,253	28,614
Total cost	602,115	501,866
Owned Properties | Irving Texas
Real Estate Properties [Line Items]
Land	8,606	8,606
Buildings, Improvements and Equipment	345,615	276,894
Construction in progress	99,445	86,320
Total cost	453,666	371,820
Owned Properties | Richmond, Virginia
Real Estate Properties [Line Items]
Land	2,180	2,180
Buildings, Improvements and Equipment	253,098	254,603
Construction in progress	67,932	61,888
Total cost	323,210	318,671
Owned Properties | Chicago, Illinois
Real Estate Properties [Line Items]
Land	9,400	9,400
Buildings, Improvements and Equipment	130,150	81,463
Construction in progress	133,095	135,479
Total cost	272,645	226,342
Owned Properties | Ashburn, Virginia
Real Estate Properties [Line Items]
Land	17,325
Buildings, Improvements and Equipment	63,245
Construction in progress	184,951	106,952
Total cost	265,521	106,952
Owned Properties | Suwanee, Georgia (Atlanta-Suwanee)
Real Estate Properties [Line Items]
Land	3,521	3,521
Buildings, Improvements and Equipment	166,298	165,915
Construction in progress	3,188	3,620
Total cost	173,007	173,056
Owned Properties | Piscataway New Jersey
Real Estate Properties [Line Items]
Land	7,466	7,466
Buildings, Improvements and Equipment	97,806	83,251
Construction in progress	33,472	37,807
Total cost	138,744	128,524
Owned Properties | Manassas, Virginia
Real Estate Properties [Line Items]
Construction in progress	45,194
Total cost	45,194
Owned Properties | Manassas, Virginia | Assets Held For Sale
Real Estate Properties [Line Items]
Construction in progress	71,000
Owned Properties | Santa Clara, California
Real Estate Properties [Line Items]
Buildings, Improvements and Equipment	98,548	100,028
Construction in progress	7,600	6,989
Total cost	106,148	107,017
Owned Properties | Dulles, Virginia
Real Estate Properties [Line Items]
Land	3,154	3,154
Buildings, Improvements and Equipment	72,435	76,239
Construction in progress	3,852	3,565
Total cost	79,441	82,958
Owned Properties | Fort Worth, Texas
Real Estate Properties [Line Items]
Land	9,079	9,079
Buildings, Improvements and Equipment	18,623	17,894
Construction in progress	43,715	33,774
Total cost	71,417	60,747
Owned Properties | Sacramento, California
Real Estate Properties [Line Items]
Land	1,481	1,481
Buildings, Improvements and Equipment	64,874	64,251
Construction in progress	92	58
Total cost	66,447	65,790
Owned Properties | Princeton, New Jersey
Real Estate Properties [Line Items]
Land	20,700	20,700
Buildings, Improvements and Equipment	34,046	32,948
Construction in progress	431	451
Total cost	55,177	54,099
Owned Properties | Hillsboro, Oregon
Real Estate Properties [Line Items]
Construction in progress	39,835	29,278
Total cost	39,835	29,278
Owned Properties | Phoenix, Arizona
Real Estate Properties [Line Items]
Construction in progress	29,562	27,402
Total cost	29,562	27,402
Owned Properties | Other
Real Estate Properties [Line Items]
Land	2,213	2,213
Buildings, Improvements and Equipment	35,720	35,505
Construction in progress	113	88
Total cost	$ 38,046	$ 37,806
Leased Properties
Real Estate Properties [Line Items]
Number of facilities leased | property	10	11
Leased Properties | Owned Properties
Real Estate Properties [Line Items]
Buildings, Improvements and Equipment	$ 43,347	$ 59,460
Construction in progress	9,334	5,534
Total cost	$ 52,681	$ 64,994