CONSOLIDATED STATEMENTS OF EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Total Stockholders' Equity	Preferred Stock	Common Shares	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Member's Equity	Noncontrolling Interests	Redeemable Noncontrolling Interests
Balance at Dec. 31, 2009	$ 162,338	$ 162,338						$ 162,338
Increase (Decrease) in Stockholders' Equity
Contributions	33,399	33,399						33,399
Distributions	(2,000)	(2,000)						(2,000)
Initial capitalization of CoreSite Realty Corporation (in shares)				1,000
Issuance of common stock	310,960	310,960		194	310,766
Issuance of common stock (in shares)				19,435,000
Issuance of Operating Partnership units in exchange for 100% of the interests in our predecessor	(236,764)	(236,764)						(236,764)		236,764
Issuance of Operating Partnership units in exchange for 100% of the interests in the CoreSite Acquired Properties										316,836
Redemption of Operating Partnership units for cash										(125,513)
Offering costs	(25,306)	(25,306)			(25,306)
Reclassify member's equity to additional paid in capital					(43,027)			43,027
Issuance of stock awards	361	361			361
Issuance of stock awards (in shares)				208,042
Issuance of equity incentive Operating Partnership units										975
Amortization of deferred compensation	538	538			538
Dividends and distributions	(5,967)	(2,554)				(2,554)			(3,413)
Adjustment to reflect redeemable noncontrolling interest at redemption value	(3,879)	(3,879)			(3,879)					3,879
Net income (loss)	(9,181)	(4,906)				(4,906)			(4,275)	(3,096)
Unrealized gain (loss) on derivative contracts	121	52					52		69
Reclassify redeemable noncontrolling interests to permanent equity	429,845								429,845	(429,845)
Balance at Dec. 31, 2010	654,465	232,239		194	239,453	(7,460)	52		422,226
Balance (in shares) at Dec. 31, 2010				19,644,042
Increase (Decrease) in Stockholders' Equity
Offering costs	(17)	(17)			(17)
Redemption of noncontrolling interests		13,768		9	13,759				(13,768)
Redemption of noncontrolling interests (in shares)				889,610
Issuance of restricted stock awards, net of forfeitures (in shares)				212,180
Exercise of stock options	31	31			31
Exercise of stock options (in shares)				1,962
Amortization of deferred compensation	2,958	2,958		1	2,957
Dividends and distributions	(26,278)	(11,474)				(11,474)			(14,804)
Net income (loss)	(10,779)	(4,611)				(4,611)			(6,168)
Unrealized gain (loss) on derivative contracts	(366)	(163)					(163)		(203)
Reclassification of other comprehensive loss to interest expense	173	77					77		96
Balance at Dec. 31, 2011	620,187	232,808		204	256,183	(23,545)	(34)		387,379
Balance (in shares) at Dec. 31, 2011				20,747,794
Increase (Decrease) in Stockholders' Equity
Issuance of restricted stock awards, net of forfeitures (in shares)				357,009
Exercise of stock options	1,564	1,564		1	1,563
Exercise of stock options (in shares)				97,870
Issuance of Series A Preferred Stock	110,615	110,615	115,000		(4,385)
Amortization of deferred compensation	5,650	5,650		2	5,648
Dividends accumulated on preferred stock	(440)	(440)				(440)
Dividends and distributions	(37,592)	(17,050)				(17,050)			(20,542)
Net income (loss)	10,716	5,048				5,048			5,668
Unrealized gain (loss) on derivative contracts	(72)	(31)					(31)		(41)
Reclassification of other comprehensive loss to interest expense	145	65					65		80
Balance at Dec. 31, 2012	$ 710,773	$ 338,229	$ 115,000	$ 207	$ 259,009	$ (35,987)			$ 372,544
Balance (in shares) at Dec. 31, 2012				21,202,673