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Marketable Securities (Tables)
 3 Months Ended
Apr. 30, 2019
Investments Debt And Equity Securities [Abstract]  
Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value of Available-For-Sale Securities The amortized cost, gross unrealized gains (losses) and fair value of available-for-sale securities by major security type and class of security as of April 30, 2019, January 31, 2019 and April 30, 2018 were as follows:

 

 

 

Amortized

 

 

Unrealized

 

 

Unrealized

 

 

Fair

 

 

 

Cost

 

 

Gains

 

 

(Losses)

 

 

Value

 

As of April 30, 2019

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Short-term Investments:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Corporate bonds

 

$

169,627

 

 

$

72

 

 

$

(70

)

 

$

169,629

 

Municipal and pre-refunded municipal bonds

 

 

52,131

 

 

 

23

 

 

 

(6

)

 

 

52,148

 

Federal government agencies

 

 

2,735

 

 

 

4

 

 

 

—

 

 

 

2,739

 

Certificates of deposit

 

 

1,650

 

 

 

—

 

 

 

—

 

 

 

1,650

 

Commercial paper

 

 

2,997

 

 

 

—

 

 

 

—

 

 

 

2,997

 

 

 

 

229,140

 

 

 

99

 

 

 

(76

)

 

 

229,163

 

Long-term Investments:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Corporate bonds

 

 

71,105

 

 

 

95

 

 

 

(46

)

 

 

71,154

 

Municipal and pre-refunded municipal bonds

 

 

11,035

 

 

 

11

 

 

 

(8

)

 

 

11,038

 

Mutual funds, held in rabbi trust

 

 

7,733

 

 

 

208

 

 

 

 

 

 

 

7,941

 

Federal government agencies

 

 

2,351

 

 

 

7

 

 

 

—

 

 

 

2,358

 

Certificates of deposit

 

 

1,403

 

 

 

—

 

 

 

—

 

 

 

1,403

 

 

 

 

93,627

 

 

 

321

 

 

 

(54

)

 

 

93,894

 

 

 

$

322,767

 

 

$

420

 

 

$

(130

)

 

$

323,057

 

As of January 31, 2019

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Short-term Investments:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Corporate bonds

 

$

227,287

 

 

$

24

 

 

$

(214

)

 

$

227,097

 

Municipal and pre-refunded municipal bonds

 

 

43,677

 

 

 

15

 

 

 

(18

)

 

 

43,674

 

Federal government agencies

 

 

1,458

 

 

 

—

 

 

 

—

 

 

 

1,458

 

Certificates of deposit

 

 

1,050

 

 

 

—

 

 

 

—

 

 

 

1,050

 

Commercial paper

 

 

2,979

 

 

 

—

 

 

 

—

 

 

 

2,979

 

Treasury bills

 

 

2,975

 

 

 

—

 

 

 

(1

)

 

 

2,974

 

 

 

 

279,426

 

 

 

39

 

 

 

(233

)

 

 

279,232

 

Long-term Investments:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Corporate bonds

 

 

34,265

 

 

 

34

 

 

 

(63

)

 

 

34,236

 

Municipal and pre-refunded municipal bonds

 

 

7,554

 

 

 

7

 

 

 

(3

)

 

 

7,558

 

Mutual funds, held in rabbi trust

 

 

6,301

 

 

 

450

 

 

 

—

 

 

 

6,751

 

Federal government agencies

 

 

6,603

 

 

 

2

 

 

 

(1

)

 

 

6,604

 

Certificates of deposit

 

 

2,143

 

 

 

—

 

 

 

—

 

 

 

2,143

 

 

 

 

56,866

 

 

 

493

 

 

 

(67

)

 

 

57,292

 

 

 

$

336,292

 

 

$

532

 

 

$

(300

)

 

$

336,524

 

 

 

Amortized

 

 

Unrealized

 

 

Unrealized

 

 

Fair

 

 

 

Cost

 

 

Gains

 

 

(Losses)

 

 

Value

 

As of April 30, 2018

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Short-term Investments:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Corporate bonds

 

$

110,657

 

 

$

—

 

 

$

(294

)

 

$

110,363

 

Municipal and pre-refunded municipal bonds

 

 

54,659

 

 

 

—

 

 

 

(47

)

 

 

54,612

 

Certificates of deposit

 

 

1,392

 

 

 

—

 

 

 

—

 

 

 

1,392

 

 

 

 

166,708

 

 

 

—

 

 

 

(341

)

 

 

166,367

 

Long-term Investments:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Corporate bonds

 

 

18,137

 

 

 

—

 

 

 

(212

)

 

 

17,925

 

Municipal and pre-refunded municipal bonds

 

 

7,873

 

 

 

—

 

 

 

(30

)

 

 

7,843

 

Mutual funds, held in rabbi trust

 

 

6,453

 

 

 

33

 

 

 

(3

)

 

 

6,483

 

Certificates of deposit

 

 

2,828

 

 

 

—

 

 

 

—

 

 

 

2,828

 

 

 

 

35,291

 

 

 

33

 

 

 

(245

)

 

 

35,079

 

 

 

$

201,999

 

 

$

33

 

 

$

(586

)

 

$

201,446