Short-Term Investments - Schedule of Short-Term Investments (Detail) - USD ($)
$ in Thousands |
Apr. 30, 2018 |
Jan. 31, 2018 |
| Schedule of Available-for-sale Securities [Line Items] |
|
|
|
| Available-for-sale securities, Amortized cost |
$ 460,070
|
$ 443,272
|
|
| Available-for-sale securities, Gross unrealized gains |
34
|
7
|
|
| Available-for-sale securities, Gross unrealized losses |
(2,035)
|
(1,500)
|
|
| Available-for-sale securities, Estimated fair value |
458,069
|
441,779
|
[1] |
| Certificates of deposits [Member] |
|
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
|
| Available-for-sale securities, Amortized cost |
11,030
|
|
|
| Available-for-sale securities, Gross unrealized gains |
4
|
|
|
| Available-for-sale securities, Estimated fair value |
11,034
|
|
|
| Asset-backed securities [Member] |
|
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
|
| Available-for-sale securities, Amortized cost |
70,068
|
67,875
|
|
| Available-for-sale securities, Gross unrealized gains |
1
|
|
|
| Available-for-sale securities, Gross unrealized losses |
(615)
|
(424)
|
|
| Available-for-sale securities, Estimated fair value |
69,454
|
67,451
|
|
| Commercial paper [Member] |
|
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
|
| Available-for-sale securities, Amortized cost |
21,286
|
19,926
|
|
| Available-for-sale securities, Gross unrealized gains |
1
|
|
|
| Available-for-sale securities, Gross unrealized losses |
(9)
|
(12)
|
|
| Available-for-sale securities, Estimated fair value |
21,278
|
19,914
|
|
| Corporate notes and bonds [Member] |
|
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
|
| Available-for-sale securities, Amortized cost |
155,457
|
160,499
|
|
| Available-for-sale securities, Gross unrealized gains |
24
|
1
|
|
| Available-for-sale securities, Gross unrealized losses |
(1,011)
|
(759)
|
|
| Available-for-sale securities, Estimated fair value |
154,470
|
159,741
|
|
| Foreign government bonds [Member] |
|
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
|
| Available-for-sale securities, Amortized cost |
1,503
|
1,504
|
|
| Available-for-sale securities, Gross unrealized losses |
(23)
|
(18)
|
|
| Available-for-sale securities, Estimated fair value |
1,480
|
1,486
|
|
| Mortgage backed securities [Member] |
|
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
|
| Available-for-sale securities, Amortized cost |
13,027
|
11,555
|
|
| Available-for-sale securities, Gross unrealized gains |
2
|
|
|
| Available-for-sale securities, Gross unrealized losses |
(100)
|
(75)
|
|
| Available-for-sale securities, Estimated fair value |
12,929
|
11,480
|
|
| U.S. agency obligations [Member] |
|
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
|
| Available-for-sale securities, Amortized cost |
64,765
|
71,206
|
|
| Available-for-sale securities, Gross unrealized gains |
1
|
1
|
|
| Available-for-sale securities, Gross unrealized losses |
(59)
|
(76)
|
|
| Available-for-sale securities, Estimated fair value |
64,707
|
71,131
|
|
| U.S. treasury securities [Member] |
|
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
|
| Available-for-sale securities, Amortized cost |
122,934
|
110,707
|
|
| Available-for-sale securities, Gross unrealized gains |
1
|
5
|
|
| Available-for-sale securities, Gross unrealized losses |
(218)
|
(136)
|
|
| Available-for-sale securities, Estimated fair value |
$ 122,717
|
$ 110,576
|
|
|
|