Investments in Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	$ 204,441	$ 257,500
Gross Unrealized Gains	668	4,125
Gross Unrealized Losses	(3,199)	(7,526)
Fair Value	201,910	254,099
Total Investments	200,192	248,954
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Corporate notes and bonds	190,197	248,954
Total Investments	200,192	248,954
Other Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Securities, Fair Value	1,718	5,145
US Government and Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	10,007
Gross Unrealized Gains	0
Gross Unrealized Losses	(12)
Fair Value	9,995
US Government and Agency Securities [Member] | Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Corporate notes and bonds	9,995
Corporate Notes and Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Amortized Cost Basis	190,496	253,590
Debt Securities, Gross Unrealized Gains	0	0
Debt Securities, Gross Unrealized Losses	(299)	(4,636)
Debt Securities, Fair Value	190,197	248,954
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Securities, Amortized Cost Basis	3,938	3,910
Equity Securities, Gross Unrealized Gains	668	4,125
Equity Securities, Gross Unrealized Losses	(2,888)	(2,890)
Equity Securities, Fair Value	$ 1,718	$ 5,145