Real Estate Assets and Construction in Progress (Summary of Properties Owned or Leased by the Company) (Details) $ in Thousands	Sep. 30, 2016 USD ($) property	Dec. 31, 2015 USD ($) property
Real Estate Properties [Line Items]
Land	$ 73,968	$ 57,112
Buildings, improvements and equipment	1,449,376	1,180,386
Construction in progress	320,650	345,655
Total cost	1,843,994	1,583,153
Owned Properties [Member]
Real Estate Properties [Line Items]
Land	72,838	55,982
Buildings, improvements and equipment	1,332,530	1,061,247
Construction in progress	311,516	336,034
Total cost	1,716,884	1,453,263
Owned Properties [Member] | Suwanee, Georgia (Atlanta-Suwanee) [Member]
Real Estate Properties [Line Items]
Land	3,521	3,521
Buildings, improvements and equipment	155,443	150,028
Construction in progress	16,130	15,330
Total cost	175,094	168,879
Owned Properties [Member] | Atlanta, Georgia (Atlanta-Metro) [Member]
Real Estate Properties [Line Items]
Land	15,397	15,397
Buildings, improvements and equipment	432,302	406,190
Construction in progress	30,338	41,835
Total cost	478,037	463,422
Owned Properties [Member] | Santa Clara, California [Member]
Real Estate Properties [Line Items]
Buildings, improvements and equipment	97,170	94,437
Construction in progress	5,731	1,379
Total cost	102,901	95,816
Owned Properties [Member] | Richmond, Virginia [Member]
Real Estate Properties [Line Items]
Land	2,180	2,180
Buildings, improvements and equipment	236,610	208,654
Construction in progress	68,270	85,771
Total cost	307,060	296,605
Owned Properties [Member] | Sacramento, California [Member]
Real Estate Properties [Line Items]
Land	1,481	1,481
Buildings, improvements and equipment	61,905	61,462
Construction in progress	222	73
Total cost	63,608	63,016
Owned Properties [Member] | Princeton, New Jersey [Member]
Real Estate Properties [Line Items]
Land	20,700	20,700
Buildings, improvements and equipment	32,776	32,708
Construction in progress	500	422
Total cost	53,976	53,830
Owned Properties [Member] | Dallas-Fort Worth, Texas [Member]
Real Estate Properties [Line Items]
Land	8,606	8,590
Buildings, improvements and equipment	152,575	71,783
Construction in progress	99,637	120,331
Total cost	260,818	200,704
Owned Properties [Member] | Chicago, Illinois [Member]
Real Estate Properties [Line Items]
Land	9,400
Buildings, improvements and equipment	45,393
Construction in progress	74,277	70,749
Total cost	129,070	70,749
Owned Properties [Member] | Miami, Florida [Member]
Real Estate Properties [Line Items]
Land	1,777	1,777
Buildings, improvements and equipment	31,089	30,554
Construction in progress	74	144
Total cost	32,940	32,475
Owned Properties [Member] | Lenexa, Kansas [Member]
Real Estate Properties [Line Items]
Land	437	437
Buildings, improvements and equipment	3,733	3,511
Construction in progress	0
Total cost	4,170	3,948
Owned Properties [Member] | Deluth, Georgia [Member]
Real Estate Properties [Line Items]
Land	1,899	1,899
Buildings, improvements and equipment	1,896	1,920
Construction in progress	1,611
Total cost	5,406	3,819
Owned Properties [Member] | Piscataway New Jersey [Member]
Real Estate Properties [Line Items]
Land	7,440
Buildings, improvements and equipment	81,638
Construction in progress	14,726
Total cost	103,804
Leased Properties [Member]
Real Estate Properties [Line Items]
Land	1,130	1,130
Buildings, improvements and equipment	116,846	119,139
Construction in progress	9,134	9,621
Total cost	127,110	129,890
Leased Properties [Member] | Jersey City, New Jersey [Member]
Real Estate Properties [Line Items]
Buildings, improvements and equipment	22,853	28,228
Construction in progress	2,232	2,421
Total cost	25,085	30,649
Leased Properties [Member] | Overland Park, Kansas [Member]
Real Estate Properties [Line Items]
Buildings, improvements and equipment	959	922
Construction in progress	8	4
Total cost	967	926
Leased Properties [Member] | Carpathia Properties [Member]
Real Estate Properties [Line Items]
Land	1,130	1,130
Buildings, improvements and equipment	93,034	89,989
Construction in progress	6,894	7,196
Total cost	$ 101,058	$ 98,315
Number of facilities leased | property	12	13