Accounts Receivable - Additional Information (Detail) - Trade Accounts Receivable [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of accounts receivable	$ 18,973	$ 25,146	$ 57,185
Selling, General and Administrative Expenses [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Pre-tax losses on accounts receivable	$ 55	$ 78	$ 114