Investments in Available-for-Sale Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Current	$ 249,067	$ 248,414
Total Investments, Cost Basis	258,233	255,046
Total Investments, Accumulated Gross Unrealized Gains	10,258	13,678
Total Investments, Accumulated Gross Unrealized Losses	(6,506)	(4,281)
Total Investments	261,985	264,443
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Investments, Current	249,067	248,414
Other Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Investments, Noncurrent	12,918	16,029
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Cost Basis	0	65,002
Debt Securities, Accumulated Gross Unrealized Gains	0	11
Debt Securities, Accumulated Gross Unrealized Losses	0	(75)
Debt Securities	0	64,938
US Treasury and Government [Member] | Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Current	0	64,938
US Treasury and Government [Member] | Other Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Noncurrent	0	0
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Cost Basis	252,813	184,773
Debt Securities, Accumulated Gross Unrealized Gains	1	7
Debt Securities, Accumulated Gross Unrealized Losses	(3,747)	(1,304)
Debt Securities	249,067	183,476
Corporate Debt Securities [Member] | Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Current	249,067	183,476
Corporate Debt Securities [Member] | Other Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Noncurrent	0	0
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Securities, Cost Basis	5,420	5,271
Equity Securities, Accumulated Gross Unrealized Gains	10,257	13,660
Equity Securities, Accumulated Gross Unrealized Losses	(2,759)	(2,902)
Equity securities	12,918	16,029
Equity Securities [Member] | Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Securities, Current	0	0
Equity Securities [Member] | Other Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Securities, Noncurrent	$ 12,918	$ 16,029