Organization - Additional Information (Detail)	Sep. 30, 2018 store state
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating storage facilities in which the entity has equity interests (in stores)	1,099
Number of stores owned by franchisees and third parties	507
Number of operating stores owned and/or managed	1,606
Number of states in which operating storage facilities are located | state	39