Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013 security	Dec. 31, 2012
Investments
Cost Basis, Securities included in deposits and other assets	$ 625	$ 625
Estimated Fair Value, Securities included in deposits and other assets	625	625
Cost Basis	527,873	271,569
Unrealized Gains	37,535	22,581
Unrealized Losses	(619)	(185)
Other-Than-Temporary Impairment Loss	(880)	(880)
Estimated Fair Value	563,909	293,085
Temporarily impaired investments
Temporarily impaired securities, Number of Investments	163
Temporarily impaired securities, Less than 12 months of temporary impairment, Estimated Fair Value	269,870
Less than 12 months of temporary impairment, Unrealized Losses	(607)
Temporarily impaired securities, More than 12 months of temporary impairment, Estimated Fair Value	12,358
More than 12 months of temporary impairment, Unrealized Losses	(12)
Total temporary impairment, Estimated Fair Value	282,228
Total temporary impairment, Unrealized Losses	(619)
Available-for-sale securities:
Investments
Amortized Cost	510,184	253,839
Unrealized Gains	347	310
Unrealized Losses	(619)	(185)
Estimated Fair Value	509,912	253,964
Available-for-sale securities: | Debt maturities of one year or less
Investments
Amortized Cost	179,659	144,909
Unrealized Gains	109	102
Unrealized Losses	(71)	(77)
Estimated Fair Value	179,697	144,934
Available-for-sale securities: | Debt maturities of more than one year
Investments
Amortized Cost	330,525	108,930
Unrealized Gains	238	208
Unrealized Losses	(548)	(108)
Estimated Fair Value	330,215	109,030
Corporate debt securities
Temporarily impaired investments
Temporarily impaired securities, Number of Investments	148
Temporarily impaired securities, Less than 12 months of temporary impairment, Estimated Fair Value	213,469
Less than 12 months of temporary impairment, Unrealized Losses	(412)
Temporarily impaired securities, More than 12 months of temporary impairment, Estimated Fair Value	8,228
More than 12 months of temporary impairment, Unrealized Losses	(8)
Total temporary impairment, Estimated Fair Value	221,697
Total temporary impairment, Unrealized Losses	(420)
Corporate debt securities | Debt maturities of one year or less
Investments
Amortized Cost	142,096	115,249
Unrealized Gains	75	81
Unrealized Losses	(27)	(9)
Estimated Fair Value	142,144	115,321
Corporate debt securities | Debt maturities of more than one year
Investments
Amortized Cost	265,969	80,166
Unrealized Gains	177	112
Unrealized Losses	(393)	(92)
Estimated Fair Value	265,753	80,186
Debt securities issued by U.S. government agencies
Temporarily impaired investments
Temporarily impaired securities, Number of Investments	8
Temporarily impaired securities, Less than 12 months of temporary impairment, Estimated Fair Value	49,437
Less than 12 months of temporary impairment, Unrealized Losses	(143)
Total temporary impairment, Estimated Fair Value	49,437
Total temporary impairment, Unrealized Losses	(143)
Debt securities issued by U.S. government agencies | Debt maturities of one year or less
Investments
Amortized Cost	23,242	12,100
Unrealized Gains	22	2
Unrealized Losses	(16)	(66)
Estimated Fair Value	23,248	12,036
Debt securities issued by U.S. government agencies | Debt maturities of more than one year
Investments
Amortized Cost	41,308	8,034
Unrealized Gains	3	38
Unrealized Losses	(127)
Estimated Fair Value	41,184	8,072
Debt securities issued by the U.S. Treasury | Debt maturities of one year or less
Investments
Amortized Cost	6,239	1,000
Unrealized Gains	6	1
Estimated Fair Value	6,245	1,001
Debt securities issued by the U.S. Treasury | Debt maturities of more than one year
Investments
Amortized Cost	9,062	12,424
Unrealized Gains	21	27
Estimated Fair Value	9,083	12,451
Debt securities issued by states of the United States and political subdivisions of the states
Temporarily impaired investments
Temporarily impaired securities, Number of Investments	7
Temporarily impaired securities, Less than 12 months of temporary impairment, Estimated Fair Value	6,964
Less than 12 months of temporary impairment, Unrealized Losses	(52)
Temporarily impaired securities, More than 12 months of temporary impairment, Estimated Fair Value	4,130
More than 12 months of temporary impairment, Unrealized Losses	(4)
Total temporary impairment, Estimated Fair Value	11,094
Total temporary impairment, Unrealized Losses	(56)
Debt securities issued by states of the United States and political subdivisions of the states | Debt maturities of one year or less
Investments
Amortized Cost	8,082	16,560
Unrealized Gains	6	18
Unrealized Losses	(28)	(2)
Estimated Fair Value	8,060	16,576
Debt securities issued by states of the United States and political subdivisions of the states | Debt maturities of more than one year
Investments
Amortized Cost	14,186	8,306
Unrealized Gains	37	31
Unrealized Losses	(28)	(16)
Estimated Fair Value	14,195	8,321
Equity securities
Investments
Cost Basis	17,689	17,730
Unrealized Gains	37,188	22,271
Other-Than-Temporary Impairment Loss	(880)	(880)
Estimated Fair Value	53,997	39,121
Equity securities | Securities included in other current assets
Investments
Cost Basis	1,538	1,579
Unrealized Gains	618	4,175
Other-Than-Temporary Impairment Loss	(880)	(880)
Estimated Fair Value	1,276	4,874
Equity securities | Regulus Therapeutics Inc.
Investments
Cost Basis	15,526	15,526
Unrealized Gains	36,570	18,096
Estimated Fair Value	$ 52,096	$ 33,622