Summary of Significant Accounting Policies - Intangibles (Detail)	12 Months Ended
	Dec. 31, 2017
Customer and Supplier Relationships [Member] | Minimum [Member]
Significant accounting policies
Amortizable period of the intangible assets	10 years
Customer and Supplier Relationships [Member] | Maximum [Member]
Significant accounting policies
Amortizable period of the intangible assets	15 years
Covenants not-to-compete [Member] | Minimum [Member]
Significant accounting policies
Amortizable period of the intangible assets	2 years
Covenants not-to-compete [Member] | Maximum [Member]
Significant accounting policies
Amortizable period of the intangible assets	5 years