Investments - Average Coupon Rate Percentage and the Average Days to Maturity of Debt (Detail) |
6 Months Ended | 12 Months Ended |
|---|---|---|
Jun. 30, 2016 |
Dec. 31, 2015 |
|
| Commercial Paper [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 0.932% | 0.553% |
| Average Days To Maturity | 279 days | 154 days |
| US Government Agencies [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 0.973% | 0.865% |
| Average Days To Maturity | 559 days | 599 days |
| Corporate Bonds and Notes [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 1.633% | 1.757% |
| Average Days To Maturity | 507 days | 331 days |