|
Summary of Significant Accounting Policies - Short-Term Investments (Detail) (USD $)
In Thousands, unless otherwise specified
|
Mar. 31, 2015
|
Dec. 31, 2014
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Gross Cost |
$ 573,003 |
$ 521,641 |
| Gross Unrealized Gains |
177 |
52 |
| Gross Unrealized Losses |
(371) |
(849) |
| Short-term Investments, fair value |
572,809 |
520,844 |
| Time Deposits [Member] |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Gross Cost |
31,781 |
21,726 |
| Short-term Investments, fair value |
31,781 |
21,726 |
| Commercial paper [Member] |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Gross Cost |
|
3,999 |
| Short-term Investments, fair value |
|
3,999 |
| U.S. government agency bonds [Member] |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Gross Cost |
15,435 |
|
| Gross Unrealized Losses |
(8) |
|
| Short-term Investments, fair value |
15,427 |
|
| Corporate bonds [Member] |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Gross Cost |
348,075 |
353,957 |
| Gross Unrealized Gains |
125 |
7 |
| Gross Unrealized Losses |
(276) |
(752) |
| Short-term Investments, fair value |
347,924 |
353,212 |
| International government bonds [Member] |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Gross Cost |
2,712 |
1,504 |
| Gross Unrealized Losses |
(3) |
(3) |
| Short-term Investments, fair value |
2,709 |
1,501 |
| Municipal bonds [Member] |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Gross Cost |
175,000 |
140,455 |
| Gross Unrealized Gains |
52 |
45 |
| Gross Unrealized Losses |
(84) |
(94) |
| Short-term Investments, fair value |
$ 174,968 |
$ 140,406 |