Fair Value Measurements (Details) (USD $)				6 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Jun. 30, 2013 Sarepta Therapeutics, Inc. [Member]	Jun. 30, 2013 Regulus Therapeutics Inc. [Member]	Jun. 30, 2014 Achaogen Inc [Member]	Jun. 30, 2014 2 3/4 percent convertible senior notes [Member]	Dec. 31, 2013 2 3/4 percent convertible senior notes [Member]	Jun. 30, 2014 Recurring basis [Member]		Dec. 31, 2013 Recurring basis [Member]		Jun. 30, 2014 Recurring basis [Member] Corporate debt securities [Member]		Dec. 31, 2013 Recurring basis [Member] Corporate debt securities [Member]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 2014 Recurring basis [Member] Equity securities [Member]		Dec. 31, 2013 Recurring basis [Member] Equity securities [Member]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 2014 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Other Observable Inputs (Level 2) [Member]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 2014 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member]		Dec. 31, 2013 Recurring basis [Member] Significant Unobservable Inputs (Level 3) [Member]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 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									70,638,000	[1]	133,233,000	[1]																					70,638,000	[1]	133,233,000	[1]																					0	[1]	0	[1]																					0	[1]	0	[1]
Available-for-sale securities													339,847,000	[1],[2]	407,897,000	[1],[2]	98,373,000	[2]	64,432,000	[2]	11,264,000	[2]	15,328,000	[2]	66,391,000	[2]	22,255,000	[2]	2,481,000	[3]	1,276,000	[3]					0	[1],[2]	0	[1],[2]	0	[2]	0	[2]	11,264,000	[2]	15,328,000	[2]	0	[2]	0	[2]	625,000	[3]	1,276,000	[3]					339,847,000	[1],[2]	407,897,000	[1],[2]	98,373,000	[2]	64,432,000	[2]	0	[2]	0	[2]	66,391,000	[2]	22,255,000	[2]	0	[3]	0	[3]					0	[1],[2]	0	[1],[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	1,856,000	[3]	0	[3]
Investment in Regulus Therapeutics Inc.	56,678,000	52,096,000							56,678,000		52,096,000																						56,678,000		52,096,000																						0		0																						0		0
Total assets									645,672,000		696,517,000																						139,205,000		201,933,000																						504,611,000		494,584,000																						1,856,000		0
Realized gain on sale of common stock				1,100,000
Gross fair value of investment					69,200,000	2,100,000
Lack of marketability discount					7,000,000	214,000
Interest rate on convertible debt (in hundredths)	2.75%	2.75%					2.75%	2.75%
Fair value of convertible notes							$ 448,300,000

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

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

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