Assets and Liabilities Measured at Fair Value on a Recurring Basis - Investments Measured at Fair Value (Detail) - USD ($) $ in Thousands		May 31, 2019		Feb. 28, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross Unrealized Gains		$ 297		$ 299
Gross Unrealized Losses		(875)	[1]	(2,661)	[2]
Available-for-sale securities, debt securities		365,797
Cash, cash equivalents and available-for-sale securities amortized cost		1,523,725		1,484,044
Cash, cash equivalents and available-for-sale securities		1,523,147		1,481,682
Accumulated unrealized losses related to investments in unrealized loss position 12 months or longer		900		2,600
Fair value of investments with unrealized losses		268,000		387,800
Cash Equivalent Marketable Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalent marketable securities		1,157,350		939,809
Investments in debt securities, short-term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities		177,625		293,361
Investments in debt securities, long-term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities		188,172		248,512
Money markets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and restricted cash		901,570		398,056
Cash and cash equivalents, fair value disclosure		901,570		398,056
Money markets | Cash Equivalent Marketable Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and restricted cash		901,570		398,056
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and restricted cash		255,780		541,753
Cash and cash equivalents, fair value disclosure		255,780		541,753
Commercial paper | Cash Equivalent Marketable Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and restricted cash		255,780		541,753
Commercial paper | Investments in debt securities, short-term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and restricted cash		0
Commercial paper | Investments in debt securities, long-term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and restricted cash				0
Corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities, amortized cost		162,629		263,059
Gross Unrealized Gains		284		299
Gross Unrealized Losses		(251)	[1]	(666)	[2]
Available-for-sale securities, debt securities		162,662		262,692
Corporate securities | Cash Equivalent Marketable Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities				0
Corporate securities | Investments in debt securities, short-term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities		108,943		161,441
Corporate securities | Investments in debt securities, long-term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities		53,719		101,251
Interest-bearing deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities, amortized cost				56,883
Gross Unrealized Gains				0
Gross Unrealized Losses	[2]			0
Available-for-sale securities, debt securities				56,883
Interest-bearing deposits | Investments in debt securities, short-term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities				56,883
Interest-bearing deposits | Investments in debt securities, long-term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities				0
U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities, amortized cost		203,746		224,293
Gross Unrealized Gains		13		0
Gross Unrealized Losses		(624)	[1]	(1,995)	[2]
Available-for-sale securities, debt securities		203,135		222,298
U.S. agency securities | Investments in debt securities, short-term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities		68,682		75,037
U.S. agency securities | Investments in debt securities, long-term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities		$ 134,453		$ 147,261

[1] As of May 31, 2019, there were $0.9 million of accumulated unrealized losses related to investments that have been in a continuous unrealized loss position for 12 months or longer. The aggregate related fair value of investments with unrealized losses was $268.0 million.

[2] As of February 28, 2019, there were $2.6 million of accumulated unrealized losses related to investments that have been in a continuous unrealized loss position for 12 months or longer. The aggregate related fair value of investments with unrealized losses was $387.8 million.