Noncontrolling Interest (Details)	0 Months Ended	9 Months Ended			0 Months Ended	9 Months Ended				9 Months Ended
	Jun. 19, 2013 property	Sep. 30, 2013	Sep. 30, 2013 Operating Partnership	Dec. 31, 2012 Operating Partnership	Jun. 19, 2013 Noncontrolling Common Units property	Sep. 30, 2013 Noncontrolling Common Units Operating Partnership	Dec. 31, 2012 Noncontrolling Common Units Operating Partnership	Sep. 30, 2013 LTIP Units Operating Partnership	Dec. 31, 2012 LTIP Units Operating Partnership	Sep. 30, 2013 LTIP Units Operating Partnership 2011 Plan
Noncontrolling interest
Units held by noncontrolling interests (in shares)						6,299,186	5,743,958	599,464	413,551
Ownership interest held by noncontrolling owners (as a percent)			13.54%	14.71%
Redemption right of investor to cause the Operating Partnership to redeem its units equivalent to current market value of number of shares of entity's common stock (in shares)						1
Conversion ratio of noncontrolling units						1				1
Number of common units issued as a consideration for purchase of building	555,758				555,758
Number of buildings purchased through issuance of common stock	8				8
Noncontrolling common units converted to common stock (in shares)		2,186