CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended		9 Months Ended
	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Sep. 27, 2010 Predecessor
Operating revenues:
Rental revenue	$ 24,428	$ 123,397	$ 108,597	$ 24,377
Power revenue	9,403	53,563	43,402	8,520
Interconnection revenue	2,553	20,887	12,161	803
Tenant reimbursement and other	1,968	9,087	8,686	1,857
Total operating revenues	38,352	206,934	172,846	35,557
Operating expenses:
Property operating and maintenance	12,107	61,235	55,049	14,272
Real estate taxes and insurance	1,642	8,765	9,119	1,262
Management fees to related party				3,582
Depreciation and amortization	19,146	64,327	68,967	11,848
Sales and marketing	1,341	10,330	5,744	125
General and administrative	4,987	25,910	21,846	2,258
Rent	4,551	18,711	18,336	2,177
Transaction costs	3,275	613	875
Total operating expenses	47,049	189,891	179,936	35,524
Operating income (loss)	(8,697)	17,043	(7,090)	33
Gain on early extinguishment of debt			939
Interest income	77	13	117	2
Interest expense	(2,325)	(5,236)	(5,275)	(1,590)
Income (loss) before income taxes	(10,945)	11,820	(11,309)	(1,555)
Income tax (expense) benefit	223	(1,104)	530
Net income (loss)	(10,722)	10,716	(10,779)	(1,555)
Net income (loss) attributable to noncontrolling interests	(7,371)	5,668	(6,168)
Net income (loss) attributable to CoreSite Realty Corporation	(3,351)	5,048	(4,611)	(1,555)
Preferred stock dividends		(440)
Net income(loss) attributable to common shares	$ (3,351)	$ 4,608	$ (4,611)	$ (1,555)
Net income (loss) per share attributable to common shares:
Basic (in dollars per share)	$ (0.17)	$ 0.22	$ (0.24)
Diluted (in dollars per share)	$ (0.17)	$ 0.22	$ (0.24)
Weighted average common shares outstanding
Basic (in shares)	19,458,605	20,537,946	19,609,375
Diluted (in shares)	19,458,605	20,992,290	19,609,375