Real Estate Assets and Construction in Progress (Summary of Properties Owned or Leased by the Company) (Details) $ in Thousands	Sep. 30, 2018 USD ($) property	Dec. 31, 2017 USD ($) property
Real Estate Properties [Line Items]
Land	$ 105,541	$ 88,216
Buildings, Improvements and Equipment	1,881,390	1,701,287
Construction in progress	731,660	567,819
Total cost	$ 2,718,591	$ 2,357,322
Number of facilities leased | property	11	11
Owned Properties | Atlanta, Georgia (Atlanta-Metro)
Real Estate Properties [Line Items]
Land	$ 20,416	$ 20,416
Buildings, Improvements and Equipment	492,825	452,836
Construction in progress	9,702	28,614
Total cost	522,943	501,866
Owned Properties | Irving Texas
Real Estate Properties [Line Items]
Land	8,606	8,606
Buildings, Improvements and Equipment	326,900	276,894
Construction in progress	109,431	86,320
Total cost	444,937	371,820
Owned Properties | Richmond, Virginia
Real Estate Properties [Line Items]
Land	2,180	2,180
Buildings, Improvements and Equipment	252,549	254,603
Construction in progress	67,021	61,888
Total cost	321,750	318,671
Owned Properties | Chicago, Illinois
Real Estate Properties [Line Items]
Land	9,400	9,400
Buildings, Improvements and Equipment	114,981	81,463
Construction in progress	138,140	135,479
Total cost	262,521	226,342
Owned Properties | Suwanee, Georgia (Atlanta-Suwanee)
Real Estate Properties [Line Items]
Land	3,521	3,521
Buildings, Improvements and Equipment	163,828	165,915
Construction in progress	4,586	3,620
Total cost	171,935	173,056
Owned Properties | Ashburn, Virginia
Real Estate Properties [Line Items]
Land	17,326
Buildings, Improvements and Equipment	63,197
Construction in progress	163,296	106,952
Total cost	243,819	106,952
Owned Properties | Piscataway New Jersey
Real Estate Properties [Line Items]
Land	7,466	7,466
Buildings, Improvements and Equipment	92,052	83,251
Construction in progress	36,470	37,807
Total cost	135,988	128,524
Owned Properties | Santa Clara, California
Real Estate Properties [Line Items]
Buildings, Improvements and Equipment	98,089	100,028
Construction in progress	7,583	6,989
Total cost	105,672	107,017
Owned Properties | Dulles, Virginia
Real Estate Properties [Line Items]
Land	3,154	3,154
Buildings, Improvements and Equipment	71,893	76,239
Construction in progress	4,145	3,565
Total cost	79,192	82,958
Owned Properties | Sacramento, California
Real Estate Properties [Line Items]
Land	1,481	1,481
Buildings, Improvements and Equipment	64,772	64,251
Construction in progress	110	58
Total cost	66,363	65,790
Owned Properties | Fort Worth, Texas
Real Estate Properties [Line Items]
Land	9,078	9,079
Buildings, Improvements and Equipment	18,437	17,894
Construction in progress	38,909	33,774
Total cost	66,424	60,747
Owned Properties | Princeton, New Jersey
Real Estate Properties [Line Items]
Land	20,700	20,700
Buildings, Improvements and Equipment	33,776	32,948
Construction in progress	478	451
Total cost	54,954	54,099
Owned Properties | Phoenix, Arizona
Real Estate Properties [Line Items]
Construction in progress	29,162	27,402
Total cost	29,162	27,402
Owned Properties | Hillsboro, Oregon
Real Estate Properties [Line Items]
Construction in progress	35,867	29,278
Total cost	35,867	29,278
Owned Properties | Manassas, Virginia
Real Estate Properties [Line Items]
Construction in progress	77,529
Total cost	77,529
Owned Properties | Other
Real Estate Properties [Line Items]
Land	2,213	2,213
Buildings, Improvements and Equipment	35,586	35,505
Construction in progress	266	88
Total cost	38,065	37,806
Leased Properties | Owned Properties
Real Estate Properties [Line Items]
Buildings, Improvements and Equipment	52,505	59,460
Construction in progress	8,965	5,534
Total cost	$ 61,470	$ 64,994