Organization and operations (Details)	0 Months Ended
	Jun. 10, 2013	Mar. 31, 2015 property state	Dec. 31, 2014 property
Organization and operations
Number of properties		36,588	34,599
Number of states		22
Number of Properties Held for Sale		35
Operating Partnership | Series D Convertible Units
Organization and operations
Units issued to AH LLC (in shares)	4,375,000
Operating Partnership | Series E Convertible Units
Organization and operations
Units issued to AH LLC (in shares)	4,375,000