Real Estate - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017
Real Estate Properties [Line Items]
Weighted average lease term remaining	48 months
Minimum lease payments on leases periods	Greater than one year
Minimum [Member]
Real Estate Properties [Line Items]
Operating leases lease term	1 year
Maximum [Member]
Real Estate Properties [Line Items]
Operating leases lease term	65 years