Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value of Available-For-Sale Securities (Detail) - USD ($) $ in Thousands	Apr. 30, 2018	Jan. 31, 2018	Apr. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 201,999	$ 224,005	$ 156,932
Unrealized Gains	33	293	110
Unrealized (Losses)	(586)	(485)	(98)
Fair Value	201,446	223,813	156,944
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	166,708	165,337	118,526
Unrealized Gains		11	28
Unrealized (Losses)	(341)	(223)	(61)
Fair Value	166,367	165,125	118,493
Short-term Investments \| Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	110,657	111,612	77,313
Unrealized Gains			4
Unrealized (Losses)	(294)	(184)	(58)
Fair Value	110,363	111,428	77,259
Short-term Investments \| Municipal And Pre-Refunded Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	54,659	52,474	40,788
Unrealized Gains		11	24
Unrealized (Losses)	(47)	(39)	(3)
Fair Value	54,612	52,446	40,809
Short-term Investments \| Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,392	1,251	425
Fair Value	1,392	1,251	425
Long Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	35,291	58,668	38,406
Unrealized Gains	33	282	82
Unrealized (Losses)	(245)	(262)	(37)
Fair Value	35,079	58,688	38,451
Long Term Investments \| Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,137	39,853	27,586
Unrealized Gains			3
Unrealized (Losses)	(212)	(228)	(36)
Fair Value	17,925	39,625	27,553
Long Term Investments \| Municipal And Pre-Refunded Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,873	9,873	4,758
Unrealized Gains		8	17
Unrealized (Losses)	(30)	(24)
Fair Value	7,843	9,857	4,775
Long Term Investments \| Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,828	2,969	1,051
Fair Value	2,828	2,969	1,051
Long Term Investments \| Mutual Funds, Held in Rabbi Trust
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,453	5,973	5,011
Unrealized Gains	33	274	62
Unrealized (Losses)	(3)	(10)	(1)
Fair Value	$ 6,483	$ 6,237	$ 5,072

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

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+ References

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