Summary of Significant Accounting Policies - Estimated Useful Lives of Assets (Detail)	12 Months Ended
	Dec. 31, 2014
Tenant improvements [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of the assets	Shorter of economic life or lease terms
Minimum [Member] | Buildings [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of the assets	20 years
Minimum [Member] | Building improvements and fixtures [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of the assets	5 years
Maximum [Member] | Buildings [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of the assets	31 years 6 months
Maximum [Member] | Building improvements and fixtures [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of the assets	20 years