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Reconciliation of Recurring Fair Value Measurements Recognized in Balance Sheet using Significant Unobservable (Level Three) Inputs (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Beginning balance $ 2,454 $ 2,645 $ 2,539
Total realized and unrealized gains (losses)      
Included in net income   (193) (416)
Included in other comprehensive income (loss) 30 (56) 540
Purchases, issuances and settlements (9) 58 (18)
Ending balance 2,475 2,454 2,645
Total gains or losses for the period included in net income attributable to the change in unrealized gains or losses related to assets still held at the reporting date   $ (193) $ (416)