Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments	$ 56,678	$ 37,133
Cash Equivalents [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Cash Equivalents	185,068	226,130
Cash Equivalents [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Cash Equivalents	1,097	998
Cash Equivalents [Member] | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Cash Equivalents	4,791	2,000
Short-Term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments	56,678	37,133
Short-Term Investments [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments	15,019	9,612
Short-Term Investments [Member] | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments	21,951	19,703
Short-Term Investments [Member] | U.S. Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments	2,101	4,501
Short-Term Investments [Member] | Corporate Bonds and Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments	8,473	3,317
Short-Term Investments [Member] | International Government Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments	9,134
Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash Equivalents [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Cash Equivalents	185,068	226,130
Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash Equivalents [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Cash Equivalents
Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash Equivalents [Member] | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Cash Equivalents
Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Short-Term Investments [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments
Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Short-Term Investments [Member] | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments
Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Short-Term Investments [Member] | U.S. Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments
Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Short-Term Investments [Member] | Corporate Bonds and Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments
Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Short-Term Investments [Member] | International Government Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments
Fair Value Measurements Using Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Cash Equivalents
Fair Value Measurements Using Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Cash Equivalents	1,097	998
Fair Value Measurements Using Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents [Member] | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Cash Equivalents	4,791	2,000
Fair Value Measurements Using Significant Other Observable Inputs (Level 2) [Member] | Short-Term Investments [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments	15,019	9,612
Fair Value Measurements Using Significant Other Observable Inputs (Level 2) [Member] | Short-Term Investments [Member] | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments	21,951	19,703
Fair Value Measurements Using Significant Other Observable Inputs (Level 2) [Member] | Short-Term Investments [Member] | U.S. Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments	2,101	4,501
Fair Value Measurements Using Significant Other Observable Inputs (Level 2) [Member] | Short-Term Investments [Member] | Corporate Bonds and Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments	8,473	3,317
Fair Value Measurements Using Significant Other Observable Inputs (Level 2) [Member] | Short-Term Investments [Member] | International Government Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments	9,134
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) [Member] | Cash Equivalents [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Cash Equivalents
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) [Member] | Cash Equivalents [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Cash Equivalents
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) [Member] | Cash Equivalents [Member] | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Cash Equivalents
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) [Member] | Short-Term Investments [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) [Member] | Short-Term Investments [Member] | Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) [Member] | Short-Term Investments [Member] | U.S. Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) [Member] | Short-Term Investments [Member] | Corporate Bonds and Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) [Member] | Short-Term Investments [Member] | International Government Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets-Short-Term Investments