Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014 Investment	Dec. 31, 2013
Investments
Cost Basis	$ 533,243	$ 527,873
Unrealized Gains	43,434	37,535
Unrealized Losses	(374)	(619)
Other-Than-Temporary Impairment Loss	(1,269)	(880)
Estimated Fair Value	575,034	563,909
Temporarily impaired investments [Abstract]
Temporarily impaired securities, Number of Investments	159
Temporarily impaired securities, Less than 12 months of temporary impairment, Estimated Fair Value	206,215
Less than 12 months of temporary impairment, Unrealized Losses	(363)
Temporarily impaired securities, More than 12 months of temporary impairment, Estimated Fair Value	8,342
More than 12 months of temporary impairment, Unrealized Losses	(11)
Total temporary impairment, Estimated Fair Value	214,557
Total temporary impairment, Unrealized Losses	(374)
Available-for-sale securities [Member]
Investments
Amortized Cost	515,823	510,184
Unrealized Gains	426	347
Unrealized Losses	(374)	(619)
Other-Than-Temporary Impairment Loss	0	0
Estimated Fair Value	515,875	509,912
Available-for-sale securities [Member] | Debt maturities of one year or less [Member]
Investments
Amortized Cost	280,828	179,659
Unrealized Gains	163	109
Unrealized Losses	(119)	(71)
Other-Than-Temporary Impairment Loss	0	0
Estimated Fair Value	280,872	179,697
Available-for-sale securities [Member] | Debt maturities of more than one year [Member]
Investments
Amortized Cost	234,995	330,525
Unrealized Gains	263	238
Unrealized Losses	(255)	(548)
Other-Than-Temporary Impairment Loss	0	0
Estimated Fair Value	235,003	330,215
Corporate debt securities [Member]
Temporarily impaired investments [Abstract]
Temporarily impaired securities, Number of Investments	135
Temporarily impaired securities, Less than 12 months of temporary impairment, Estimated Fair Value	130,498
Less than 12 months of temporary impairment, Unrealized Losses	(167)
Temporarily impaired securities, More than 12 months of temporary impairment, Estimated Fair Value	8,342
More than 12 months of temporary impairment, Unrealized Losses	(11)
Total temporary impairment, Estimated Fair Value	138,840
Total temporary impairment, Unrealized Losses	(178)
Corporate debt securities [Member] | Debt maturities of one year or less [Member]
Investments
Amortized Cost	166,635	142,096	[1]
Unrealized Gains	115	75	[1]
Unrealized Losses	(39)	(27)	[1]
Other-Than-Temporary Impairment Loss	0	0	[1]
Estimated Fair Value	166,711	142,144	[1]
Corporate debt securities [Member] | Debt maturities of more than one year [Member]
Investments
Amortized Cost	173,089	265,969
Unrealized Gains	186	177
Unrealized Losses	(139)	(393)
Other-Than-Temporary Impairment Loss	0	0
Estimated Fair Value	173,136	265,753
Debt securities issued by U.S. government agencies [Member]
Temporarily impaired investments [Abstract]
Temporarily impaired securities, Number of Investments	12
Temporarily impaired securities, Less than 12 months of temporary impairment, Estimated Fair Value	65,917
Less than 12 months of temporary impairment, Unrealized Losses	(114)
Temporarily impaired securities, More than 12 months of temporary impairment, Estimated Fair Value	0
More than 12 months of temporary impairment, Unrealized Losses	0
Total temporary impairment, Estimated Fair Value	65,917
Total temporary impairment, Unrealized Losses	(114)
Debt securities issued by U.S. government agencies [Member] | Debt maturities of one year or less [Member]
Investments
Amortized Cost	61,421	23,242	[1]
Unrealized Gains	14	22	[1]
Unrealized Losses	(38)	(16)	[1]
Other-Than-Temporary Impairment Loss	0	0	[1]
Estimated Fair Value	61,397	23,248	[1]
Debt securities issued by U.S. government agencies [Member] | Debt maturities of more than one year [Member]
Investments
Amortized Cost	37,048	41,308
Unrealized Gains	4	3
Unrealized Losses	(76)	(127)
Other-Than-Temporary Impairment Loss	0	0
Estimated Fair Value	36,976	41,184
Debt securities issued by the U.S. Treasury [Member] | Debt maturities of one year or less [Member]
Investments
Amortized Cost	9,245	6,239
Unrealized Gains	17	6
Unrealized Losses	0	0
Other-Than-Temporary Impairment Loss	0	0
Estimated Fair Value	9,262	6,245
Debt securities issued by the U.S. Treasury [Member] | Debt maturities of more than one year [Member]
Investments
Amortized Cost	1,997	9,062
Unrealized Gains	5	21
Unrealized Losses	0	0
Other-Than-Temporary Impairment Loss	0	0
Estimated Fair Value	2,002	9,083
Debt securities issued by states of the United States and political subdivisions of the states [Member]
Temporarily impaired investments [Abstract]
Temporarily impaired securities, Number of Investments	12
Temporarily impaired securities, Less than 12 months of temporary impairment, Estimated Fair Value	9,800
Less than 12 months of temporary impairment, Unrealized Losses	(82)
Temporarily impaired securities, More than 12 months of temporary impairment, Estimated Fair Value	0
More than 12 months of temporary impairment, Unrealized Losses	0
Total temporary impairment, Estimated Fair Value	9,800
Total temporary impairment, Unrealized Losses	(82)
Debt securities issued by states of the United States and political subdivisions of the states [Member] | Debt maturities of one year or less [Member]
Investments
Amortized Cost	43,527	8,082
Unrealized Gains	17	6
Unrealized Losses	(42)	(28)
Other-Than-Temporary Impairment Loss	0	0
Estimated Fair Value	43,502	8,060
Debt securities issued by states of the United States and political subdivisions of the states [Member] | Debt maturities of more than one year [Member]
Investments
Amortized Cost	22,861	14,186
Unrealized Gains	68	37
Unrealized Losses	(40)	(28)
Other-Than-Temporary Impairment Loss	0	0
Estimated Fair Value	22,889	14,195
Equity securities [Member]
Investments
Cost Basis	17,420	17,689
Unrealized Gains	43,008	37,188
Unrealized Losses	0	0
Other-Than-Temporary Impairment Loss	(1,269)	(880)
Estimated Fair Value	59,159	53,997
Equity securities [Member] | Securities included in other current assets [Member]
Investments
Cost Basis	1,269	1,538
Unrealized Gains	1,856	618
Unrealized Losses	0	0
Other-Than-Temporary Impairment Loss	(1,269)	(880)
Estimated Fair Value	1,856	1,276
Equity securities [Member] | Securities included in deposits and other assets [Member]
Investments
Cost Basis, Securities included in deposits and other assets	625	625
Estimated Fair Value, Securities included in deposits and other assets	625	625
Unrealized Gains	0	0
Unrealized Losses	0	0
Other-Than-Temporary Impairment Loss	0	0
Equity securities [Member] | Regulus Therapeutics Inc. [Member]
Investments
Cost Basis	15,526	15,526
Unrealized Gains	41,152	36,570
Unrealized Losses	0	0
Other-Than-Temporary Impairment Loss	0	0
Estimated Fair Value	$ 56,678	$ 52,096

[1] Includes investments classified as cash equivalents on our consolidated balance sheet.