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Investments - Gains Unrealized Gains and (Losses) Aggregated by Investment Category Short-Term and Long-Term Securities (Detail) (USD $) In Thousands, unless otherwise specified | Jun. 30, 2013 | Dec. 31, 2012
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | $ 345,792 |
Investments, Gross Unrealized Gains | 27 |
Investments, Gross Unrealized (Losses) | (18) |
Short-term investments, Estimated Fair Value | 345,801 | 326,862
Long-term investments, Estimated Fair Value | 15,788 | 12,158
Bankers' Acceptance Drafts [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Short-term investments, Estimated Fair Value | 145 | 242
Time Deposits [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Short-term investments, Estimated Fair Value | 52,157 | 52
Long-term investments, Estimated Fair Value | 54 |
Commercial Paper [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Short-term investments, Estimated Fair Value | 46,495 |
U.S. Treasury Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Short-term investments, Estimated Fair Value | 5,004 | 13,054
U.S. Agency Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Short-term investments, Estimated Fair Value | 242,000 | 313,514
Long-term investments, Estimated Fair Value | 15,734 | 12,158
Short Term [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost |  | 326,601
Investments, Gross Unrealized Gains |  | 267
Investments, Gross Unrealized (Losses) |  | (6)
Short Term [Member] | Bankers' Acceptance Drafts [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 145 | 242
Short Term [Member] | Time Deposits [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 52,157 | 52
Short Term [Member] | Commercial Paper [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 46,495 |
Short Term [Member] | U.S. Treasury Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 5,003 | 13,045
Investments, Gross Unrealized Gains | 1 | 9
Short Term [Member] | U.S. Agency Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 241,992 | 313,262
Investments, Gross Unrealized Gains | 26 | 258
Investments, Gross Unrealized (Losses) | (18) | (6)
Long Term [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 15,790 |
Investments, Gross Unrealized Gains | 1 |
Investments, Gross Unrealized (Losses) | (3) |
Long Term [Member] | Time Deposits [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 54 |
Long Term [Member] | U.S. Agency Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 15,736 | 12,156
Investments, Gross Unrealized Gains | 1 | 2
Investments, Gross Unrealized (Losses) | $ (3) |

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- Definition Amount of accumulated pre-tax unrealized gains before deducting pre-tax unrealized losses on investments in available-for-sale securities impacting investments. + References No definition available. + Details
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