Fair Value Hierarchy For Financial Assets And Liabilities Measured At Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	$ 12,008,060	$ 11,395,728
Investment in joint venture, fair value	33,226	32,745
Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	68,247	70,086
Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	5,844,099	5,522,215
Investment in joint venture, fair value	0	0
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	6,095,714	5,803,427
Investment in joint venture, fair value	0	0
Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Convertible debt	(2,534,038)	(2,665,690)
Convertible Debt | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Convertible debt
Convertible Debt | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Convertible debt	(2,534,038)	(2,665,690)
Convertible Debt | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Convertible debt
Private Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	325,437	351,855
Private Equity Securities [Member] | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	325,437	351,855
Private Equity Securities [Member] | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Private Equity Securities [Member] | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Publicly Traded Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	110,071	86,482
Publicly Traded Equity Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Publicly Traded Equity Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Publicly Traded Equity Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	110,071	86,482
Foreign Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	1,415,463	1,273,023
Foreign Debt Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Foreign Debt Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	1,415,463	1,273,023
Foreign Debt Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Auction Rate Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	68,247	70,086
Auction Rate Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	68,247	70,086
Auction Rate Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Auction Rate Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Municipal Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	971,293	1,022,889
Municipal Obligations | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Municipal Obligations | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	971,293	1,022,889
Municipal Obligations | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Asset-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	3,730	2,117
Asset-backed Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Asset-backed Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	3,730	2,117
Asset-backed Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
High Yield Corporate Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	529,059	510,412
High Yield Corporate Debt Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
High Yield Corporate Debt Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	529,059	510,412
High Yield Corporate Debt Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
US Corporate Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	1,520,806	1,480,450
US Corporate Debt Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
US Corporate Debt Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	1,520,806	1,480,450
US Corporate Debt Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
US Government Agencies Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	2,085,086	2,196,209
US Government Agencies Debt Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
US Government Agencies Debt Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	947,477	871,290
US Government Agencies Debt Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	1,137,609	1,324,919
Foreign Exchange Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign exchange derivative assets	22,261	30,189
Foreign exchange derivative liabilities	(40,403)	(34,590)
Foreign Exchange Contract | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign exchange derivative assets
Foreign exchange derivative liabilities
Foreign Exchange Contract | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign exchange derivative assets	22,261	30,189
Foreign exchange derivative liabilities	(40,403)	(34,590)
Foreign Exchange Contract | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign exchange derivative assets
Foreign exchange derivative liabilities
Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative liabilities	75	(588)
Commodity Contract | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative liabilities
Commodity Contract | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative liabilities	75	(588)
Commodity Contract | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative liabilities
Cash Equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	3,682,131	3,260,217
Cash Equivalents | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Cash Equivalents | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	456,271	362,034
Cash Equivalents | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	3,225,860	2,898,183
Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	1,622,174	1,493,843
Cash | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Cash | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Cash | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	$ 1,622,174	$ 1,493,843