Summary of Significant Accounting Policies - Property and Equipment at Cost Using Straight-Line Method (Detail)	12 Months Ended
	Dec. 31, 2017
Buildings and leasehold improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life, Years	3 years
Buildings and leasehold improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life, Years	40 years
Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life, Years	3 years
Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life, Years	10 years
Furniture and fixtures [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life, Years	5 years
Furniture and fixtures [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life, Years	10 years
Transportation equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life, Years	3 years
Transportation equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life, Years	20 years