Fair Value Measurements - Schedule of Investments at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands | Jun. 30, 2015 | Dec. 31, 2014 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets held in rabbi trust | $ 5,627 | $ 4,332 |
Marketable securities, available for sale | 102,864 | 14,752 |
Short-term investments [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 51,070 | |
Short-term investments [Member] | U.S. Treasuries [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 31,944 | |
Short-term investments [Member] | U.S. Government Sponsored Entities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 19,126 | |
Long-term marketable securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 51,794 | 14,752 |
Long-term marketable securities [Member] | U.S. Treasuries [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 12,496 | 2,981 |
Long-term marketable securities [Member] | U.S. Government Sponsored Entities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 11,801 | 2,016 |
Long-term marketable securities [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 16,946 | 7,478 |
Long-term marketable securities [Member] | Asset-backed securities and other [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 10,551 | 2,277 |
Recurring [Member] | Money market funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents | 7,205 | 25,310 |
Recurring [Member] | Assets held in rabbi trust [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets held in rabbi trust | 5,627 | 4,332 |
Recurring [Member] | Short-term investments [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 51,070 | |
Recurring [Member] | Short-term investments [Member] | U.S. Treasuries [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 31,944 | |
Recurring [Member] | Short-term investments [Member] | U.S. Government Sponsored Entities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 19,126 | |
Recurring [Member] | Long-term marketable securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 51,794 | 14,752 |
Recurring [Member] | Long-term marketable securities [Member] | U.S. Treasuries [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 12,496 | 2,980 |
Recurring [Member] | Long-term marketable securities [Member] | U.S. Government Sponsored Entities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 11,801 | 2,017 |
Recurring [Member] | Long-term marketable securities [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 16,946 | 7,478 |
Recurring [Member] | Long-term marketable securities [Member] | Asset-backed securities and other [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 10,551 | 2,277 |
Level 1 [Member] | Recurring [Member] | Money market funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents | 7,205 | 25,310 |
Level 1 [Member] | Recurring [Member] | Short-term investments [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 31,944 | |
Level 1 [Member] | Recurring [Member] | Short-term investments [Member] | U.S. Treasuries [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 31,944 | |
Level 1 [Member] | Recurring [Member] | Long-term marketable securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 12,496 | 2,980 |
Level 1 [Member] | Recurring [Member] | Long-term marketable securities [Member] | U.S. Treasuries [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 12,496 | 2,980 |
Level 2 [Member] | Recurring [Member] | Assets held in rabbi trust [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets held in rabbi trust | 5,627 | 4,332 |
Level 2 [Member] | Recurring [Member] | Short-term investments [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 19,126 | |
Level 2 [Member] | Recurring [Member] | Short-term investments [Member] | U.S. Government Sponsored Entities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 19,126 | |
Level 2 [Member] | Recurring [Member] | Long-term marketable securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 39,298 | 11,772 |
Level 2 [Member] | Recurring [Member] | Long-term marketable securities [Member] | U.S. Government Sponsored Entities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 11,801 | 2,017 |
Level 2 [Member] | Recurring [Member] | Long-term marketable securities [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 16,946 | 7,478 |
Level 2 [Member] | Recurring [Member] | Long-term marketable securities [Member] | Asset-backed securities and other [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | $ 10,551 | $ 2,277 |