Financial Assets and Liabilities - Short-term investments (Details) $ in Thousands		Jul. 31, 2015 USD ($)
Cash equivalents
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, cost		$ 359,833
Gross unrealized gains		0
Gross unrealized losses less than 12 months		0
Gross unrealized losses 12 months or longer		0
Estimated fair value	[1]	359,833
Cash equivalents | Money market funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, cost		357,485
Gross unrealized gains		0
Gross unrealized losses less than 12 months		0
Gross unrealized losses 12 months or longer		0
Estimated fair value	[1]	357,485
Cash equivalents | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, cost		2,348
Gross unrealized gains		0
Gross unrealized losses less than 12 months		0
Gross unrealized losses 12 months or longer		0
Estimated fair value	[1]	2,348
Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, cost		136,507
Gross unrealized gains		22
Gross unrealized losses less than 12 months		(33)
Gross unrealized losses 12 months or longer		0
Estimated fair value	[1]	136,496
Short-term investments | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, cost		10,287
Gross unrealized gains		0
Gross unrealized losses less than 12 months		0
Gross unrealized losses 12 months or longer		0
Estimated fair value	[1]	10,287
Short-term investments | U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, cost		16,605
Gross unrealized gains		4
Gross unrealized losses less than 12 months		(2)
Gross unrealized losses 12 months or longer		0
Estimated fair value	[1]	16,607
Short-term investments | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, cost		1,403
Gross unrealized gains		2
Gross unrealized losses less than 12 months		0
Gross unrealized losses 12 months or longer		0
Estimated fair value	[1]	1,405
Short-term investments | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, cost		7,800
Gross unrealized gains		0
Gross unrealized losses less than 12 months		0
Gross unrealized losses 12 months or longer		0
Estimated fair value	[1]	7,800
Short-term investments | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, cost		70,451
Gross unrealized gains		11
Gross unrealized losses less than 12 months		(22)
Gross unrealized losses 12 months or longer		0
Estimated fair value	[1]	70,440
Short-term investments | Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, cost		29,961
Gross unrealized gains		5
Gross unrealized losses less than 12 months		(9)
Gross unrealized losses 12 months or longer		0
Estimated fair value	[1]	$ 29,957

[1] See Note 6. Fair Value Measures for further discussion on fair values of cash equivalents and short-term investments.