Fair Value Measurements - Schedule of Investments at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands | Sep. 30, 2016 | Dec. 31, 2015 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets held in rabbi trust | $ 7,309 | $ 5,661 |
Marketable securities, available for sale | 142,656 | 134,255 |
Short-term investments [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 48,377 | 79,860 |
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 | 24,878 | 62,272 |
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 | 11,513 | 17,559 |
Short-term investments [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 11,986 | 0 |
Short-term investments [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 | 0 | 29 |
Long-term marketable securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 94,279 | 54,395 |
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 | 50,698 | 15,171 |
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 | 16,014 | 12,022 |
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 | 18,769 | 16,705 |
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 | 8,798 | 10,497 |
Recurring [Member] | Money market funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Money market funds | 60,513 | 5,987 |
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 | 7,309 | 5,661 |
Recurring [Member] | Short-term investments [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 48,377 | 79,860 |
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 | 24,878 | 62,272 |
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 | 11,513 | 17,559 |
Recurring [Member] | Short-term investments [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 11,986 | 0 |
Recurring [Member] | Short-term investments [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 | 0 | 29 |
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 | 94,279 | 54,395 |
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 | 50,698 | 15,171 |
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 | 16,014 | 12,022 |
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 | 18,769 | 16,705 |
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 | 8,798 | 10,497 |
Level 1 [Member] | Recurring [Member] | Money market funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Money market funds | 60,513 | 5,987 |
Level 1 [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 | 0 | 0 |
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 | 24,878 | 62,272 |
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 | 24,878 | 62,272 |
Level 1 [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 | 0 | 0 |
Level 1 [Member] | Recurring [Member] | Short-term investments [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 0 | 0 |
Level 1 [Member] | Recurring [Member] | Short-term investments [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 | 0 | 0 |
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 | 50,698 | 15,171 |
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 | 50,698 | 15,171 |
Level 1 [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 | 0 | 0 |
Level 1 [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 | 0 | 0 |
Level 1 [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 | 0 | 0 |
Level 2 [Member] | Recurring [Member] | Money market funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Money market funds | 0 | 0 |
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 | 7,309 | 5,661 |
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 | 23,499 | 17,588 |
Level 2 [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 | 0 | 0 |
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 | 11,513 | 17,559 |
Level 2 [Member] | Recurring [Member] | Short-term investments [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 11,986 | 0 |
Level 2 [Member] | Recurring [Member] | Short-term investments [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 | 0 | 29 |
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 | 43,581 | 39,224 |
Level 2 [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 | 0 | 0 |
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 | 16,014 | 12,022 |
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 | 18,769 | 16,705 |
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 | 8,798 | 10,497 |
Level 3 [Member] | Recurring [Member] | Money market funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Money market funds | 0 | 0 |
Level 3 [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 | 0 | 0 |
Level 3 [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 | 0 | 0 |
Level 3 [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 | 0 | 0 |
Level 3 [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 | 0 | 0 |
Level 3 [Member] | Recurring [Member] | Short-term investments [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities, available for sale | 0 | 0 |
Level 3 [Member] | Recurring [Member] | Short-term investments [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 | 0 | 0 |
Level 3 [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 | 0 | 0 |
Level 3 [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 | 0 | 0 |
Level 3 [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 | 0 | 0 |
Level 3 [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 | 0 | 0 |
Level 3 [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 | $ 0 | $ 0 |