Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in money market and short term treasury instruments	$ 143,410	$ 148,985
Retained interest in entities	11,042	10,707
Total, net	154,452	159,692
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in money market and short term treasury instruments	143,410	148,985
Total, net	143,410	148,985
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Retained interest in entities	11,042	10,707
Total, net	$ 11,042	$ 10,707