Basis of Presentation (Cash Cash Equivalents and Short-term Investments) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
Dec. 31, 2014	Mar. 31, 2014
Amortized Cost Basis	$ 152,275	$ 151,854
Available-for-sale Securities, Gross Unrealized Gain	58	55
Gross Unrealized Losses	(221)	(96)
Total available-for-sale investments, estimated fair value	152,112us-gaap_AvailableForSaleSecurities	151,813us-gaap_AvailableForSaleSecurities
Reported as:
Cash equivalents	16,821us-gaap_CashEquivalentsAtCarryingValue	32,611us-gaap_CashEquivalentsAtCarryingValue
Short-term investments	135,291us-gaap_ShortTermInvestments	47,181us-gaap_ShortTermInvestments
Long-term investments	0us-gaap_LongTermInvestments	72,021us-gaap_LongTermInvestments
Contractual maturities of investments:
Investments due within one year	120,291EGHT_InvestmentsDueWithinOneYear	79,792EGHT_InvestmentsDueWithinOneYear
Investments due after one year	31,821EGHT_InvestmentsDueAfterOneYear	72,021EGHT_InvestmentsDueAfterOneYear
Money Market Funds
Amortized Cost Basis	16,821	32,611
Available-for-sale Securities, Gross Unrealized Gain	0	0
Gross Unrealized Losses	0	0
Total available-for-sale investments, estimated fair value	16,821	32,611
Mutual Funds
Amortized Cost Basis	2,000	1,964
Available-for-sale Securities, Gross Unrealized Gain	0	0
Gross Unrealized Losses	(129)	(55)
Total available-for-sale investments, estimated fair value	1,871	1,909
Commercial Paper
Amortized Cost Basis	22,948	30,374
Available-for-sale Securities, Gross Unrealized Gain	4	5
Gross Unrealized Losses	0	0
Total available-for-sale investments, estimated fair value	22,952	30,379
Corporate Debt
Amortized Cost Basis	71,890	63,621
Available-for-sale Securities, Gross Unrealized Gain	47	35
Gross Unrealized Losses	(22)	(39)
Total available-for-sale investments, estimated fair value	71,915	63,617
Municipal Securities
Amortized Cost Basis	5,435	5,435
Available-for-sale Securities, Gross Unrealized Gain	3	5
Gross Unrealized Losses	(7)	(1)
Total available-for-sale investments, estimated fair value	5,431	5,439
Asset Backed Securities
Amortized Cost Basis	23,598	17,049
Available-for-sale Securities, Gross Unrealized Gain	2	6
Gross Unrealized Losses	(6)	(1)
Total available-for-sale investments, estimated fair value	23,594	17,054
Mortgage Backed Securities
Amortized Cost Basis	6,583
Available-for-sale Securities, Gross Unrealized Gain	0
Gross Unrealized Losses	(56)
Total available-for-sale investments, estimated fair value	6,527
Internatinal Government Securities
Amortized Cost Basis	800	800
Available-for-sale Securities, Gross Unrealized Gain	2	4
Gross Unrealized Losses	0	0
Total available-for-sale investments, estimated fair value	802	804
Certificates of Deposit
Amortized Cost Basis	2,200
Available-for-sale Securities, Gross Unrealized Gain	0
Gross Unrealized Losses	(1)
Total available-for-sale investments, estimated fair value	$ 2,199

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