Unbilled Trade Accounts Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 71,647	$ 135,029
Allowance for sales credit memos	(1,134)	(963)
Total accounts receivable net	70,513	134,066
Trade accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	58,278	112,106
Unbilled trade accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 13,369	$ 22,923