v3.8.0.1

Fair Value Measurements - Summary of Valuation of Investments and Financial Instruments Pricing Levels (Detail) - USD ($) $ in Thousands | Sep. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | $ 219,047 | $ 305,224
Investment Type [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 216,417 | 302,830
Investment Type [Member] | Money Market Mutual Funds [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 5,278 | 18,118
Investment Type [Member] | Commercial Paper [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 9,413 | 27,867
Investment Type [Member] | US Government Agencies [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 13,491 | 13,263
Investment Type [Member] | Corporate Bonds and Notes [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 188,235 | 243,582
Deferred Compensation Plan Assets [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 2,630 | 2,394
(Level 1) [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 7,908 | 20,512
(Level 1) [Member] | Investment Type [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 5,278 | 18,118
(Level 1) [Member] | Investment Type [Member] | Money Market Mutual Funds [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 5,278 | 18,118
(Level 1) [Member] | Deferred Compensation Plan Assets [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 2,630 | 2,394
(Level 2) [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 211,139 | 284,712
(Level 2) [Member] | Investment Type [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 211,139 | 284,712
(Level 2) [Member] | Investment Type [Member] | Commercial Paper [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 9,413 | 27,867
(Level 2) [Member] | Investment Type [Member] | US Government Agencies [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | 13,491 | 13,263
(Level 2) [Member] | Investment Type [Member] | Corporate Bonds and Notes [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total | $ 188,235 | $ 243,582

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