Real Estate Assets and Construction in Progress (Summary of Properties Owned or Leased by the Company) (Details) $ in Thousands	Dec. 31, 2016 USD ($) property	Dec. 31, 2015 USD ($) property
Real Estate Properties [Line Items]
Land	$ 74,130	$ 57,112
Buildings and improvements	1,524,767	1,180,386
Construction in progress	365,960	345,655
Total cost	1,964,857	1,583,153
Owned Properties [Member]
Real Estate Properties [Line Items]
Land	73,000	55,982
Buildings and improvements	1,407,515	1,061,247
Construction in progress	355,429	336,034
Total cost	1,835,944	1,453,263
Owned Properties [Member] | Suwanee, Georgia (Atlanta-Suwanee) [Member]
Real Estate Properties [Line Items]
Land	3,521	3,521
Buildings and improvements	171,376	150,028
Construction in progress	2,013	15,330
Total cost	176,910	168,879
Owned Properties [Member] | Atlanta, Georgia (Atlanta-Metro) [Member]
Real Estate Properties [Line Items]
Land	15,397	15,397
Buildings and improvements	434,965	406,190
Construction in progress	32,422	41,835
Total cost	482,784	463,422
Owned Properties [Member] | Santa Clara, California [Member]
Real Estate Properties [Line Items]
Buildings and improvements	98,708	94,437
Construction in progress	7,078	1,379
Total cost	105,786	95,816
Owned Properties [Member] | Richmond, Virginia [Member]
Real Estate Properties [Line Items]
Land	2,180	2,180
Buildings and improvements	237,347	208,654
Construction in progress	70,580	85,771
Total cost	310,107	296,605
Owned Properties [Member] | Sacramento, California [Member]
Real Estate Properties [Line Items]
Land	1,481	1,481
Buildings and improvements	62,102	61,462
Construction in progress	390	73
Total cost	63,973	63,016
Owned Properties [Member] | Princeton, New Jersey [Member]
Real Estate Properties [Line Items]
Land	20,700	20,700
Buildings and improvements	32,788	32,708
Construction in progress	538	422
Total cost	54,026	53,830
Owned Properties [Member] | Dallas-Fort Worth, Texas [Member]
Real Estate Properties [Line Items]
Land	8,606	8,590
Buildings and improvements	204,713	71,783
Construction in progress	69,653	120,331
Total cost	282,972	200,704
Owned Properties [Member] | Chicago, Illinois [Member]
Real Estate Properties [Line Items]
Land	9,400
Buildings and improvements	45,848
Construction in progress	100,623	70,749
Total cost	155,871	70,749
Owned Properties [Member] | Piscataway New Jersey [Member]
Real Estate Properties [Line Items]
Land	7,466
Buildings and improvements	82,210
Construction in progress	17,261
Total cost	106,937
Owned Properties [Member] | Fort Worth, Texas [Member]
Real Estate Properties [Line Items]
Land	136
Buildings and improvements	610
Construction in progress	49,116
Total cost	49,862
Owned Properties [Member] | Miami, Florida [Member]
Real Estate Properties [Line Items]
Land	1,777	1,777
Buildings and improvements	31,170	30,554
Construction in progress	83	144
Total cost	33,030	32,475
Owned Properties [Member] | Lenexa, Kansas [Member]
Real Estate Properties [Line Items]
Land	437	437
Buildings and improvements	3,760	3,511
Total cost	4,197	3,948
Owned Properties [Member] | Deluth, Georgia [Member]
Real Estate Properties [Line Items]
Land	1,899	1,899
Buildings and improvements	1,918	1,920
Construction in progress	5,672
Total cost	9,489	3,819
Leased Properties [Member]
Real Estate Properties [Line Items]
Land	1,130	1,130
Buildings and improvements	117,252	119,139
Construction in progress	10,531	9,621
Total cost	128,913	129,890
Leased Properties [Member] | Carpathia Properties [Member]
Real Estate Properties [Line Items]
Land	1,130	1,130
Buildings and improvements	92,567	89,989
Construction in progress	7,671	7,196
Total cost	$ 101,368	$ 98,315
Number of facilities leased | property	12	13
Leased Properties [Member] | Jersey City, New Jersey [Member]
Real Estate Properties [Line Items]
Buildings and improvements	$ 23,723	$ 28,228
Construction in progress	2,332	2,421
Total cost	26,055	30,649
Leased Properties [Member] | Overland Park, Kansas [Member]
Real Estate Properties [Line Items]
Buildings and improvements	962	922
Construction in progress	528	4
Total cost	$ 1,490	$ 926