Investments - Fair Value Measurements of Cash Equivalents Held in Money Market Funds and Investments (Detail) (USD $) | Sep. 30, 2014 | Dec. 31, 2013 |
In Thousands, unless otherwise specified |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | $322,572 | $365,046 |
Deferred Compensation Plan Assets [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 15,498 | 15,123 |
Corporate Bonds [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 102,520 | 166,859 |
Municipal Fixed-Rate Bonds [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 150,773 | 136,302 |
Municipal Variable Rate Demand Notes [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 18,000 | 8,310 |
Fair Value, Measurements, Recurring [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 322,572 | 365,046 |
Total | 332,433 | 368,995 |
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 51,279 | 53,575 |
Total | 61,140 | 57,524 |
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 271,293 | 311,471 |
Total | 271,293 | 311,471 |
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |
Total | ' | ' |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Cash equivalents | 9,861 | 3,949 |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Cash equivalents | 9,861 | 3,949 |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Cash equivalents | ' | ' |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Cash equivalents | ' | ' |
Fair Value, Measurements, Recurring [Member] | Deferred Compensation Plan Assets [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 15,498 | 15,123 |
Fair Value, Measurements, Recurring [Member] | Deferred Compensation Plan Assets [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 15,498 | 15,123 |
Fair Value, Measurements, Recurring [Member] | Deferred Compensation Plan Assets [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |
Fair Value, Measurements, Recurring [Member] | Deferred Compensation Plan Assets [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 102,520 | 166,859 |
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 102,520 | 166,859 |
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |
Fair Value, Measurements, Recurring [Member] | Municipal Fixed-Rate Bonds [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 150,773 | 136,302 |
Fair Value, Measurements, Recurring [Member] | Municipal Fixed-Rate Bonds [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |
Fair Value, Measurements, Recurring [Member] | Municipal Fixed-Rate Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 150,773 | 136,302 |
Fair Value, Measurements, Recurring [Member] | Municipal Fixed-Rate Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |
Fair Value, Measurements, Recurring [Member] | Municipal Variable Rate Demand Notes [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 18,000 | 8,310 |
Fair Value, Measurements, Recurring [Member] | Municipal Variable Rate Demand Notes [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |
Fair Value, Measurements, Recurring [Member] | Municipal Variable Rate Demand Notes [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 18,000 | 8,310 |
Fair Value, Measurements, Recurring [Member] | Municipal Variable Rate Demand Notes [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |
Fair Value, Measurements, Recurring [Member] | Marketable Equity Securities - Technology Industry [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 8,879 | 11,398 |
Fair Value, Measurements, Recurring [Member] | Marketable Equity Securities - Technology Industry [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 8,879 | 11,398 |
Fair Value, Measurements, Recurring [Member] | Marketable Equity Securities - Technology Industry [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |
Fair Value, Measurements, Recurring [Member] | Marketable Equity Securities - Technology Industry [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |
Fair Value, Measurements, Recurring [Member] | Marketable Equity Securities - Other [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 26,902 | 27,054 |
Fair Value, Measurements, Recurring [Member] | Marketable Equity Securities - Other [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | 26,902 | 27,054 |
Fair Value, Measurements, Recurring [Member] | Marketable Equity Securities - Other [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |
Fair Value, Measurements, Recurring [Member] | Marketable Equity Securities - Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | ' |
Schedule of Available-for-sale Securities [Line Items] | ' | ' |
Available-for-sale securities | ' | ' |