Cash Equivalents and Marketable Securities at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 2,825	$ 3,067
Total marketable securities	48,037	51,079
Government Sponsored Enterprises Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	2,000	7,999
Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	15,339	15,040
Municipal Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	30,698	28,040
Quoted Prices In Active Markets For Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	2,825	3,067
Total marketable securities	25,002	23,151
Quoted Prices In Active Markets For Identical Assets (Level 1) | Government Sponsored Enterprises Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities		2,001
Quoted Prices In Active Markets For Identical Assets (Level 1) | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	14,333	15,040
Quoted Prices In Active Markets For Identical Assets (Level 1) | Municipal Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	10,669	6,110
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	23,035	27,928
Significant Other Observable Inputs (Level 2) | Government Sponsored Enterprises Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	2,000	5,998
Significant Other Observable Inputs (Level 2) | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	1,006	0
Significant Other Observable Inputs (Level 2) | Municipal Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	$ 20,029	$ 21,930