Provision for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 22	$ 8
(Reversal of provision) provision	(22)	14
Ending Balance		22
Allowance for Doubtful Accounts | Operating leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	22	8
(Reversal of provision) provision	(22)	14
Ending Balance		$ 22