Financial instruments - aggregate accounts receivable, net of allowance for doubtful accounts (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Derivatives Fair Value [Line Items]
Accounts receivable, net		$ 345,875	$ 271,993
Spain, Italy, Portugal, and Greece
Derivatives Fair Value [Line Items]
Accounts receivable, net		$ 49,054	$ 51,098
Percentage of total net current and long-term trade accounts receivables		14.60%	19.30%
Long-term portion of trade accounts receivable, net from customers		$ 3,300	$ 2,700
Italy
Derivatives Fair Value [Line Items]
Receivables sold	$ 16,100
Proceeds from sale of receivables	$ 16,000