Schedule of Unbilled Trade Accounts Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 82,123	$ 99,219
Allowance for doubtful accounts		(31)
Allowance for sales credit memos	(1,274)	(895)
Total allowance	(1,274)	(926)
Total accounts receivable	80,849	98,293
Trade Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	63,370	77,123
Unbilled Trade Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 18,753	$ 22,096