Investments in Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Current	$ 199,731	$ 248,954
Total Investments, Cost Basis	203,377	257,500
Total Investments, Accumulated Gross Unrealized Gains	908	4,125
Total Investments, Accumulated Gross Unrealized Losses	(2,939)	(7,526)
Total Investments	201,346	254,099
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Investments, Current	199,731	248,954
Other Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Investments, Noncurrent	1,615	5,145
Corporate Notes and Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Cost Basis	199,440	253,590
Debt Securities, Accumulated Gross Unrealized Gains	359	0
Debt Securities, Accumulated Gross Unrealized Losses	(68)	(4,636)
Debt Securities	199,731	248,954
Corporate Notes and Bonds [Member] | Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Current	199,731	248,954
Corporate Notes and Bonds [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	3,937	3,910
Equity Securities, Accumulated Gross Unrealized Gains	549	4,125
Equity Securities, Accumulated Gross Unrealized Losses	(2,871)	(2,890)
Equity securities	1,615	5,145
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	$ 1,615	$ 5,145