|
Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $)
In Thousands, unless otherwise specified
|
Oct. 31, 2012
|
Jan. 31, 2012
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
$ 786,202 |
$ 100,758 |
|
Included in cash and cash equivalents [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
431,805 |
47,124 |
|
U.S. agency obligations [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
608,675 |
14,316 |
|
U.S. treasury securities [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
70,146 |
|
|
Commercial paper [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
42,697 |
23,785 |
|
Certificates of deposit [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
250 |
|
|
U.S. corporate securities [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
12,027 |
20,380 |
|
Money market funds [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
51,047 |
27,152 |
|
Municipal securities [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
1,360 |
15,125 |
|
Included in marketable securities [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
354,397 |
53,634 |
|
Level 1 [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
121,193 |
27,152 |
|
Level 1 [Member] | U.S. agency obligations [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
|
|
|
Level 1 [Member] | U.S. treasury securities [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
70,146 |
|
|
Level 1 [Member] | Commercial paper [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
|
|
|
Level 1 [Member] | Certificates of deposit [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
|
|
|
Level 1 [Member] | U.S. corporate securities [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
|
|
|
Level 1 [Member] | Money market funds [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
51,047 |
27,152 |
|
Level 1 [Member] | Municipal securities [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
|
|
|
Level 2 [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
665,009 |
73,606 |
|
Level 2 [Member] | U.S. agency obligations [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
608,675 |
14,316 |
|
Level 2 [Member] | U.S. treasury securities [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
|
|
|
Level 2 [Member] | Commercial paper [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
42,697 |
23,785 |
|
Level 2 [Member] | Certificates of deposit [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
250 |
|
|
Level 2 [Member] | U.S. corporate securities [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
12,027 |
20,380 |
|
Level 2 [Member] | Money market funds [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
|
|
|
Level 2 [Member] | Municipal securities [Member]
|
|
|
| Information about assets that are measured at fair value on a recurring basis |
|
|
| Assets Fair Value Disclosure |
$ 1,360 |
$ 15,125 |