Investments Measured at Fair Value (Detail) - USD ($) $ in Thousands		May 31, 2017		Feb. 28, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost		$ 1,406,730		$ 1,302,031
Gross Unrealized Gains		1,022		1,453
Gross Unrealized Losses		(2,278)	[1]	(2,873)	[2]
Aggregate Fair Value		1,405,474		1,300,611
Cash Equivalent Marketable Securities		326,350		258,188
Investments in debt securities, short-term		408,026		369,983	[3]
Investments in debt securities, long-term		671,098		672,440	[3]
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost		326,350		258,188
Aggregate Fair Value		326,350		258,188
Cash Equivalent Marketable Securities		326,350		258,188
Interest-bearing Deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost		27,942
Aggregate Fair Value		27,942
Investments in debt securities, short-term		27,942
Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost		20,926
Aggregate Fair Value	[4]	20,926
Investments in debt securities, short-term		20,926
U.S. Agencies Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost		334,531		329,617
Gross Unrealized Gains		14		37
Gross Unrealized Losses		(1,781)	[1]	(2,224)	[2]
Aggregate Fair Value		332,764	[4]	327,430	[5]
Investments in debt securities, short-term		27,533		27,593
Investments in debt securities, long-term		305,231		299,837
Corporate Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost		696,981		714,226
Gross Unrealized Gains		1,008		1,416
Gross Unrealized Losses		(497)	[1]	(649)	[2]
Aggregate Fair Value		697,492	[4]	714,993	[5]
Investments in debt securities, short-term		331,625		342,390
Investments in debt securities, long-term		$ 365,867		$ 372,603

[1] As of May 31, 2017, there were $0.7 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 $628.5 million.

[2] As of February 28, 2017, there were $0.6 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 $605.9 million.

[3] Derived from audited financial statements.

[4] Included in Cash and cash equivalents, Investments in debt securities, short-term or Investments in debt securities, long-term in the Company's Consolidated Balance Sheet as of May 31, 2017, in addition to $904.1 million of cash.

[5] Included in Cash and cash equivalents, Investments in debt securities, short-term or Investments in debt securities, long-term in the Company's Consolidated Balance Sheet as of February 28, 2017, in addition to $832.6 million of cash.