Annual report pursuant to Section 13 and 15(d)

Changes in Level 3 Instruments Measured on a Recurring Basis (Detail)

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Changes in Level 3 Instruments Measured on a Recurring Basis (Detail) (USD $)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance $ 405 $ 517
Transfers into (out of) Level 3      
Net realized and unrealized gains (losses):    
Transfers into (out of) Level 3      
Included in earnings (in investment income) (50) (61)
Included in accumulated other comprehensive income (pre-tax)   59
Purchases      
Settlements (138) (110)
Ending Balance 217 405
Marketable securities
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance 138 216
Transfers into (out of) Level 3      
Net realized and unrealized gains (losses):    
Transfers into (out of) Level 3      
Included in earnings (in investment income)   (27)
Included in accumulated other comprehensive income (pre-tax)   59
Purchases      
Settlements (138) (110)
Ending Balance   138
Other Long-term Investments
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance 267 301
Transfers into (out of) Level 3      
Net realized and unrealized gains (losses):    
Transfers into (out of) Level 3      
Included in earnings (in investment income) (50) (34)
Purchases      
Ending Balance $ 217 $ 267