Summary of Significant Accounting Policies - Customers with Accounts Receivable Greater than 10% (Detail) - Customer Concentration Risk [Member] - Accounts Receivable [Member]	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Walmart Stores, Inc. [Member]
Entity Wide Accounts Receivable Major Customer
Customers with accounts receivable greater than 10%		15.00%
Caterpillar Inc. [Member]
Entity Wide Accounts Receivable Major Customer
Customers with accounts receivable greater than 10%	11.60%	13.60%