Fair Value Measurements (Details) (USD $)				3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Mar. 31, 2013 Sarepta Therapeutics, Inc. [Member]	Mar. 31, 2013 Regulus Therapeutics Inc. [Member]	Mar. 31, 2014 Achaogen Inc [Member]	Mar. 31, 2014 2 3/4 percent convertible senior notes [Member]	Dec. 31, 2013 2 3/4 percent convertible senior notes [Member]	Mar. 31, 2014 Recurring basis [Member]		Dec. 31, 2013 Recurring basis [Member]		Mar. 31, 2014 Recurring basis [Member] Corporate debt securities [Member]		Dec. 31, 2013 Recurring basis [Member] Corporate debt securities [Member]		Mar. 31, 2014 Recurring basis [Member] Debt securities issued by U.S. government agencies [Member]		Dec. 31, 2013 Recurring basis [Member] Debt securities issued by U.S. government agencies [Member]		Mar. 31, 2014 Recurring basis [Member] Debt securities issued by the U.S. Treasury [Member]		Dec. 31, 2013 Recurring basis [Member] Debt securities issued by the U.S. Treasury [Member]		Mar. 31, 2014 Recurring basis [Member] Debt securities issued by states of the United States and political subdivisions of the states [Member]		Dec. 31, 2013 Recurring basis [Member] Debt securities issued by states of the United States and political subdivisions of the states [Member]		Mar. 31, 2014 Recurring basis [Member] Equity securities [Member]		Dec. 31, 2013 Recurring basis [Member] Equity securities [Member]		Mar. 31, 2014 Recurring basis [Member] Quoted Prices in Active Markets (Level 1) [Member]		Dec. 31, 2013 Recurring basis [Member] Quoted Prices in Active Markets (Level 1) [Member]		Mar. 31, 2014 Recurring basis [Member] Quoted Prices in Active Markets (Level 1) [Member] Corporate debt securities [Member]		Dec. 31, 2013 Recurring basis [Member] Quoted Prices in Active Markets (Level 1) [Member] Corporate debt securities [Member]		Mar. 31, 2014 Recurring basis [Member] Quoted Prices in Active Markets (Level 1) [Member] Debt securities issued by U.S. government agencies [Member]		Dec. 31, 2013 Recurring basis [Member] Quoted Prices in Active Markets (Level 1) [Member] Debt securities issued by U.S. government agencies [Member]		Mar. 31, 2014 Recurring basis [Member] Quoted Prices in Active Markets (Level 1) [Member] Debt securities issued by the U.S. Treasury [Member]		Dec. 31, 2013 Recurring basis [Member] Quoted Prices in Active Markets (Level 1) [Member] Debt securities issued by the U.S. Treasury [Member]		Mar. 31, 2014 Recurring basis [Member] Quoted Prices in Active Markets (Level 1) [Member] Debt securities issued by states of the United States and political subdivisions of the states [Member]		Dec. 31, 2013 Recurring basis [Member] Quoted Prices in Active Markets (Level 1) [Member] Debt securities issued by states of the United States and political subdivisions of the states [Member]		Mar. 31, 2014 Recurring basis [Member] Quoted Prices in Active Markets (Level 1) [Member] Equity securities [Member]		Dec. 31, 2013 Recurring basis [Member] Quoted Prices in Active Markets (Level 1) [Member] Equity securities [Member]		Mar. 31, 2014 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member]		Mar. 31, 2014 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member] Corporate debt securities [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member] Corporate debt securities [Member]		Mar. 31, 2014 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member] Debt securities issued by U.S. government agencies [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member] Debt securities issued by U.S. government agencies [Member]		Mar. 31, 2014 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member] Debt securities issued by the U.S. Treasury [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member] Debt securities issued by the U.S. Treasury [Member]		Mar. 31, 2014 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member] Debt securities issued by states of the United States and political subdivisions of the states [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member] Debt securities issued by states of the United States and political subdivisions of the states [Member]		Mar. 31, 2014 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member] Equity securities [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member] Equity securities [Member]		Mar. 31, 2014 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member]		Mar. 31, 2014 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member] Corporate debt securities [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member] Corporate debt securities [Member]		Mar. 31, 2014 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member] Debt securities issued by U.S. government agencies [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member] Debt securities issued by U.S. government agencies [Member]		Mar. 31, 2014 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member] Debt securities issued by the U.S. Treasury [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member] Debt securities issued by the U.S. Treasury [Member]		Mar. 31, 2014 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member] Debt securities issued by states of the United States and political subdivisions of the states [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member] Debt securities issued by states of the United States and political subdivisions of the states [Member]		Mar. 31, 2014 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member] Equity securities [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member] Equity securities [Member]
Fair Value Measurements [Abstract]
Amount of transfer between Level 1 and Level 2 investments	$ 0		$ 0
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents									149,945,000	[1]	146,357,000	[1]																					141,013,000	[1]	133,233,000	[1]																					8,932,000	[1]	13,124,000	[1]																					0	[1]	0	[1]
Available-for-sale securities													344,930,000	[2]	394,773,000	[2]	67,598,000	[2]	64,432,000	[2]	15,298,000	[2]	15,328,000	[2]	41,689,000	[2]	22,255,000	[2]	2,903,000	[3]	1,276,000	[3]					0	[2]	0	[2]	0	[2]	0	[2]	15,298,000	[2]	15,328,000	[2]	0	[2]	0	[2]	985,000	[3]	1,276,000	[3]					344,930,000	[2]	394,773,000	[2]	67,598,000	[2]	64,432,000	[2]	0	[2]	0	[2]	41,689,000	[2]	22,255,000	[2]	0	[3]	0	[3]					0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	1,918,000	[3]	0	[3]
Investment in Regulus Therapeutics Inc.	63,586,000	52,096,000							63,586,000		52,096,000																						63,586,000		52,096,000																						0		0																						0		0
Total assets									685,949,000		696,517,000																						220,882,000		201,933,000																						463,149,000		494,584,000																						1,918,000		0
Realized gain on sale of common stock				1,100,000
Gross fair value of investment					54,600,000	2,300,000
Lack of marketability discount					9,700,000	365,000
Interest rate on convertible debt (in hundredths)	2.75%	2.75%					2.75%	2.75%
Fair value of convertible notes							$ 505,200,000

[1] Included in cash and cash equivalents on our consolidated balance sheet.

[2] Included in short-term investments on our consolidated balance sheet.

[3] Included in other current assets on our consolidated balance sheet.