Investments in Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Current	$ 111,451	$ 200,192
Total Investments, Cost Basis	112,458	204,441
Total Investments, Accumulated Gross Unrealized Gains	794	668
Total Investments, Accumulated Gross Unrealized Losses	(102)	(3,199)
Total Investments	113,150	201,910
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Investments, Current	111,451	200,192
Other Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Investments, Noncurrent	1,699	1,718
US Government and Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Cost Basis	0	10,007
Debt Securities, Accumulated Gross Unrealized Gains	0	0
Debt Securities, Accumulated Gross Unrealized Losses	0	(12)
Debt Securities	0	9,995
US Government and Agency Securities [Member] | Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Current	0	9,995
US Government and Agency Securities [Member] | Other Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Noncurrent	0	0
Corporate Notes and Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Cost Basis	111,545	190,496
Debt Securities, Accumulated Gross Unrealized Gains	8	0
Debt Securities, Accumulated Gross Unrealized Losses	(102)	(299)
Debt Securities	111,451	190,197
Corporate Notes and Bonds [Member] | Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Current	111,451	190,197
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	913	3,938
Equity Securities, Accumulated Gross Unrealized Gains	786	668
Equity Securities, Accumulated Gross Unrealized Losses	0	(2,888)
Equity securities	1,699	1,718
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	$ 1,699	$ 1,718