Summary of Significant Accounting Policies - Useful Lives for Major Categories of Property and Equipment (Detail)	12 Months Ended
	Dec. 31, 2018
Buildings | Lower end
Property and Equipment [Line Items]
Property and equipment, useful life	30 years
Buildings | Upper end
Property and Equipment [Line Items]
Property and equipment, useful life	40 years
Building Improvements | Lower end
Property and Equipment [Line Items]
Property and equipment, useful life	3 years
Building Improvements | Upper end
Property and Equipment [Line Items]
Property and equipment, useful life	10 years
Furniture, Fixtures, Equipment And Purchased Software | Lower end
Property and Equipment [Line Items]
Property and equipment, useful life	3 years
Furniture, Fixtures, Equipment And Purchased Software | Upper end
Property and Equipment [Line Items]
Property and equipment, useful life	10 years