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Fair Value Measurements - Schedule of Assets and Liabilities at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets held in rabbi trust | $ 9,452 | $ 8,268 |
Marketable securities, available for sale | 211,561 | 220,645 |
Deferred compensation liability | 8,241 | 7,893 |
Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 150,752 | 137,436 |
Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 60,809 | 83,209 |
U.S. Treasuries [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 124,580 | 121,180 |
U.S. Treasuries [Member] | Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 24,423 | 45,010 |
U.S. Government Sponsored Entities [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 0 | 3,505 |
U.S. Government Sponsored Entities [Member] | Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 1,355 | 1,507 |
Corporate debt securities [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 26,172 | 11,951 |
Corporate debt securities [Member] | Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 26,471 | 31,837 |
Asset-backed securities and other [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 0 | 800 |
Asset-backed securities and other [Member] | Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 8,560 | 4,855 |
Recurring [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and cash equivalents | 190,600 | 164,725 |
Recurring [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 150,752 | 137,436 |
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 | 60,809 | 83,209 |
Recurring [Member] | Commercial Paper and Other [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and cash equivalents | 5,087 | 1,599 |
Recurring [Member] | Money market funds [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and cash equivalents | 185,513 | 163,126 |
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 | 9,452 | 8,268 |
Recurring [Member] | U.S. Treasuries [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 124,580 | 121,180 |
Recurring [Member] | U.S. Treasuries [Member] | Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 24,423 | 45,010 |
Recurring [Member] | U.S. Government Sponsored Entities [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 0 | 3,505 |
Recurring [Member] | U.S. Government Sponsored Entities [Member] | Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 1,355 | 1,507 |
Recurring [Member] | Corporate debt securities [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 26,172 | 11,951 |
Recurring [Member] | Corporate debt securities [Member] | Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 26,471 | 31,837 |
Recurring [Member] | Asset-backed securities and other [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 0 | 800 |
Recurring [Member] | Asset-backed securities and other [Member] | Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 8,560 | 4,855 |
Level 1 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Deferred compensation liability | 8,241 | 7,893 |
Level 1 [Member] | Recurring [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and cash equivalents | 185,513 | 164,725 |
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 | 124,580 | 121,180 |
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 | 24,423 | 45,010 |
Level 1 [Member] | Recurring [Member] | Commercial Paper and Other [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and cash equivalents | 0 | 1,599 |
Level 1 [Member] | Recurring [Member] | Money market funds [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and cash equivalents | 185,513 | 163,126 |
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] | U.S. Treasuries [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 124,580 | 121,180 |
Level 1 [Member] | Recurring [Member] | U.S. Treasuries [Member] | Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 24,423 | 45,010 |
Level 1 [Member] | Recurring [Member] | U.S. Government Sponsored Entities [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 1 [Member] | Recurring [Member] | U.S. Government Sponsored Entities [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 1 [Member] | Recurring [Member] | Corporate debt securities [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 1 [Member] | Recurring [Member] | Corporate debt securities [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 1 [Member] | Recurring [Member] | Asset-backed securities and other [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 1 [Member] | Recurring [Member] | Asset-backed securities and other [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 2 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Deferred compensation liability | 0 | 0 |
Level 2 [Member] | Recurring [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and cash equivalents | 5,087 | 0 |
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 | 26,172 | 16,256 |
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 | 36,386 | 38,199 |
Level 2 [Member] | Recurring [Member] | Commercial Paper and Other [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and cash equivalents | 5,087 | 0 |
Level 2 [Member] | Recurring [Member] | Money market funds [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and cash equivalents | 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 | 9,452 | 8,268 |
Level 2 [Member] | Recurring [Member] | U.S. Treasuries [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 2 [Member] | Recurring [Member] | U.S. Treasuries [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 2 [Member] | Recurring [Member] | U.S. Government Sponsored Entities [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 0 | 3,505 |
Level 2 [Member] | Recurring [Member] | U.S. Government Sponsored Entities [Member] | Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 1,355 | 1,507 |
Level 2 [Member] | Recurring [Member] | Corporate debt securities [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 26,172 | 11,951 |
Level 2 [Member] | Recurring [Member] | Corporate debt securities [Member] | Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 26,471 | 31,837 |
Level 2 [Member] | Recurring [Member] | Asset-backed securities and other [Member] | Short-term investments [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 0 | 800 |
Level 2 [Member] | Recurring [Member] | Asset-backed securities and other [Member] | Long-term marketable securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Marketable securities, available for sale | 8,560 | 4,855 |
Level 3 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Deferred compensation liability | 0 | 0 |
Level 3 [Member] | Recurring [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and cash equivalents | 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] | 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] | Commercial Paper and Other [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and cash equivalents | 0 | 0 |
Level 3 [Member] | Recurring [Member] | Money market funds [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and cash equivalents | 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 |  |
Level 3 [Member] | Recurring [Member] | U.S. Treasuries [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] | U.S. Treasuries [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] | U.S. Government Sponsored Entities [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] | U.S. Government Sponsored Entities [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] | Corporate debt securities [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] | Corporate debt securities [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] | Asset-backed securities and other [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] | Asset-backed securities and other [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 |
Contingent Consideration [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Contingent consideration | 4,788 | 2,875 | $ 0
Contingent Consideration [Member] | Level 1 [Member] | Recurring [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Contingent consideration | 0 | 0 |
Contingent Consideration [Member] | Level 2 [Member] | Recurring [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Contingent consideration | 0 | 0 |
Contingent Consideration [Member] | Level 3 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Contingent consideration | $ 4,788 | $ 2,875 |

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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563 + Details
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