v3.7.0.1

Marketable Securities - Summary of Marketable Securities (Detail) - USD ($) $ in Thousands	Apr. 30, 2017	Jan. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,017,201	$ 1,738,705
Unrealized Gains	42	269
Unrealized Losses	(1,537)	(989)
Aggregate Fair Value	2,015,706	1,737,985
U.S. agency obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,022,208	908,874
Unrealized Gains	22	179
Unrealized Losses	(1,067)	(535)
Aggregate Fair Value	1,021,163	908,518
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	254,523	192,028
Unrealized Gains	2	48
Unrealized Losses	(103)	(25)
Aggregate Fair Value	254,422	192,051
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	320,798	290,272
Unrealized Gains	18	42
Unrealized Losses	(367)	(429)
Aggregate Fair Value	320,449	289,885
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	362,364	323,106
Unrealized Gains	0	0
Unrealized Losses	0	0
Aggregate Fair Value	362,364	323,106
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	57,308	24,425
Unrealized Gains	0	0
Unrealized Losses	0	0
Aggregate Fair Value	57,308	24,425
Included in cash and cash equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	398,936	281,163
Unrealized Gains	0	0
Unrealized Losses	0	0
Aggregate Fair Value	398,936	281,163
Included in marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,618,265	1,457,542
Unrealized Gains	42	269
Unrealized Losses	(1,537)	(989)
Aggregate Fair Value	$ 1,616,770	$ 1,456,822

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

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