Investments in Available-for-Sale Securities (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	$ 255,046	$ 240,382
Gross Unrealized Gains	13,678	2,706
Gross Unrealized Losses	(4,281)	(3,436)
Fair Value	264,443	239,652
Total Investments	248,414	234,305
US Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	65,002	146,993
Available-for-sale Debt Securities Gross Unrealized Gain	12	2
Available-for-sale Debt Securities, Gross Unrealized Loss	(75)	(412)
Fair Value	64,938	146,583
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	184,773	88,118
Available-for-sale Debt Securities Gross Unrealized Gain	6
Available-for-sale Debt Securities, Gross Unrealized Loss	(1,304)	(396)
Fair Value	183,476	87,722
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	5,271	5,271
Available-for-sale Equity Securities, Gross Unrealized Gain	13,660	2,704
Available-for-sale Equity Securities, Gross Unrealized Loss	(2,902)	(2,628)
Fair Value	16,029	5,347
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
U.S. government and agency securities	64,938	146,583
Corporate notes and bonds	183,476	87,722
Total Investments	248,414	234,305
Other Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity securities	$ 16,029	$ 5,347