v3.8.0.1

Investments - Average Coupon Rate Percentage and the Average Days to Maturity of Debt (Detail) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2017 | Dec. 31, 2016
Commercial Paper [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Average Coupon Rate | 123.60% | 100.10%
Average Days To Maturity | 228 days | 184 days
US Government Agencies [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Average Coupon Rate | 121.30% | 97.00%
Average Days To Maturity | 325 days | 400 days
Corporate Bonds and Notes [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Average Coupon Rate | 171.50% | 174.50%
Average Days To Maturity | 295 days | 318 days

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- Details
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