Measured on Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2016
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	$ 1,734,380	$ 471,833
Equity Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	13,166	2,203
Government agency bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	742,256	468,630
Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	926,929	1,000
Municipal bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	41,698
Auction rate securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	9,825
Available-for-sale Securities, Other Disclosure Items [Abstract]
Value of auction rate securities for which recent auctions were unsuccessful	9,800
Par Value of auction rate securities for which recent auctions were unsuccessful	$ 22,400
Auction rate securities [Member] | Minimum
Available-for-sale Securities, Other Disclosure Items [Abstract]
Discount rate	2.00%
Liquidity risk premium (percentage)	9.10%
Anticipated liquidity horizon	7 years
Auction rate securities [Member] | Maximum
Available-for-sale Securities, Other Disclosure Items [Abstract]
Discount rate	2.50%
Liquidity risk premium (percentage)	29.50%
Anticipated liquidity horizon	10 years
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Total assets measured at fair value	$ 2,351,123	2,564,584
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Total assets measured at fair value	292,999	1,789,649
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Total assets measured at fair value	2,042,109	774,935
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Total assets measured at fair value	16,015	0
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	279,833	1,787,446
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Demand and time deposits [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	327,982	305,305
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	279,833	1,787,446
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member] | Demand and time deposits [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | Demand and time deposits [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	327,982	305,305
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member] | Demand and time deposits [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	13,166	2,203
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Government agency bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	549,737	350,081
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	756,664	1,000
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Time Deposits [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	506
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Municipal bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	30,981
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	13,166	2,203
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Government agency bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Time Deposits [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Government agency bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	549,737	350,081
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	756,664	1,000
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Time Deposits [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	506
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	30,981
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Government agency bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Time Deposits [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Government agency bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	192,519	118,549
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	170,265
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Municipal bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	10,717
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Auction rate securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	9,825
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Government agency bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Auction rate securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Government agency bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	192,519	118,549
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	164,075
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	10,717
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Auction rate securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Government agency bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0	$ 0
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	6,190
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal bonds [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	0
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Auction rate securities [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Available-for-sale Securities	9,825
Fair Value, Measurements, Recurring [Member] | Other Noncurrent Assets [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	8,928
Fair Value, Measurements, Recurring [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	0
Fair Value, Measurements, Recurring [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	8,928
Fair Value, Measurements, Recurring [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 0