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 |