Investments - Average Coupon Rate Percentage and the Average Days to Maturity of Debt (Detail) |
3 Months Ended | 12 Months Ended |
|---|---|---|
Mar. 31, 2017 |
Dec. 31, 2016 |
|
| Commercial Paper [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 1.035% | 1.001% |
| Average Days To Maturity | 140 days | 184 days |
| US Government Agencies [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 1.056% | 0.97% |
| Average Days To Maturity | 355 days | 400 days |
| Corporate Bonds and Notes [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 1.731% | 1.745% |
| Average Days To Maturity | 287 days | 318 days |