Fair Value Measurements, Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Mar. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		$ 471,833
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	$ 601,792	2,564,584
Marketable equity securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value	1,266	2,203
Corporate bonds and debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		1,000
Government agency bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		468,630
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	148,884	1,789,649
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	452,908	774,935
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	0	0
Cash Equivalents [Member] | Money market mutual funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	147,618	1,787,446
Cash Equivalents [Member] | Deposit accounts [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	452,908	305,305
Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member] | Money market mutual funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	147,618	1,787,446
Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member] | Deposit accounts [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	0	0
Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | Money market mutual funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	0	0
Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | Deposit accounts [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	452,908	305,305
Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member] | Money market mutual funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	0	0
Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member] | Deposit accounts [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	0	0
Short-term Investments [Member] | Marketable equity securities | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value	1,266	2,203
Short-term Investments [Member] | Corporate bonds and debt | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		1,000
Short-term Investments [Member] | Government agency bonds | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		350,081
Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Marketable equity securities | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value	1,266	2,203
Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate bonds and debt | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		0
Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Government agency bonds | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		0
Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Marketable equity securities | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value	0	0
Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate bonds and debt | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		1,000
Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Government agency bonds | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		350,081
Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Marketable equity securities | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value	$ 0	0
Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate bonds and debt | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		0
Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Government agency bonds | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		0
Other Long-term Investments [Member] | Government agency bonds | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		118,549
Other Long-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Government agency bonds | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		0
Other Long-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Government agency bonds | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		118,549
Other Long-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Government agency bonds | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale, estimated fair value		$ 0