Schedule of Accumulated Other-than-Temporary Credit-related Impairments Charged to Retained Earnings and Other Income (Expense), Net (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Accumulated impairments, net, attributable to assets still held at September 30, 2012	$ 58
Accumulated impairments, net, attributable to assets still held at September 30, 2012	824
Accumulated impairments, net, attributable to assets still held at September 30, 2012	$ 882