Fair Value Measurement (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Mar. 31, 2014
Cash equivalents:
Money market funds	$ 16,821	$ 32,611
Short-term investments:
Mutual funds	1,871EGHT_MutualFunds	1,909EGHT_MutualFunds
Commercial paper	22,952EGHT_CommercialPaperInvestment	30,379EGHT_CommercialPaperInvestment
Corporate debt	71,915EGHT_CorporateDebt	14,893EGHT_CorporateDebt
Certificates of deposit	2,199	0
Long-term investments:
Corporate debt	0EGHT_CorporateDebtLongTerm	48,724EGHT_CorporateDebtLongTerm
Municipal securities	5,431	5,439
Asset backed securities	23,594	17,054
Mortgage backed securities	6,527	0
International government securities	802EGHT_InternationalGovernmentSecurities	804EGHT_InternationalGovernmentSecurities
Total	152,112us-gaap_AssetsFairValueDisclosure	151,813us-gaap_AssetsFairValueDisclosure
Quoted Prices in Active Markets for Identical Assets (Level 1)
Cash equivalents:
Money market funds	16,821	32,611
Short-term investments:
Mutual funds	1,871	1,909
Commercial paper	0	0
Corporate debt	0	0
Certificates of deposit	0	0
Long-term investments:
Corporate debt	0	0
Municipal securities	0	0
Asset backed securities	0	0
Mortgage backed securities	0	0
International government securities	0	0
Total	18,692	34,520
Other Observable Inputs (Level 2)
Cash equivalents:
Money market funds	0	0
Short-term investments:
Mutual funds	0	0
Commercial paper	22,952	30,379
Corporate debt	71,915	14,893
Certificates of deposit	2,199	0
Long-term investments:
Corporate debt	0	48,724
Municipal securities	5,431	5,439
Asset backed securities	23,594	17,054
Mortgage backed securities	6,527	0
International government securities	802	804
Total	133,420	117,293
Significant Unobservable Inputs (Level 3)
Cash equivalents:
Money market funds	0	0
Short-term investments:
Mutual funds	0	0
Commercial paper	0	0
Corporate debt	0	0
Certificates of deposit	0	0
Long-term investments:
Corporate debt	0	0
Municipal securities	0	0
Asset backed securities	0	0
Mortgage backed securities	0	0
International government securities	0	0
Total	$ 0	$ 0

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