Financial Instruments (Available-for-sale Securities) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Current	$ 285,726		$ 285,726		$ 0
Cost	289,268		289,268		15,050
Gross Unrealized Gains	746		746		364
Gross Unrealized Losses	(190)		(190)		0
Fair Value	289,824		289,824		15,414
Net unrealized gains on available-for-sale securities	357		357		233
Income tax on gains from available-for-sale securities	199		199		131
Proceeds from sales and maturities of securities	1,019	$ 0	16,056	$ 342,045
Gross realized gains	0	0	3,795	1,311
Gross realized losses	0	$ 0	0	$ (99)
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Cost	3,804		3,804		15,050
Gross Unrealized Gains	294		294		364
Gross Unrealized Losses	0		0		0
Fair Value	4,098		4,098		$ 15,414
Corporate bond securities
Schedule of Available-for-sale Securities [Line Items]
Cost	194,310		194,310
Gross Unrealized Gains	306		306
Gross Unrealized Losses	(171)		(171)
Fair Value	194,445		194,445
US Treasury and Government
Schedule of Available-for-sale Securities [Line Items]
Cost	55,073		55,073
Gross Unrealized Gains	80		80
Gross Unrealized Losses	(2)		(2)
Fair Value	55,151		55,151
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Cost	36,081		36,081
Gross Unrealized Gains	66		66
Gross Unrealized Losses	(17)		(17)
Fair Value	$ 36,130		$ 36,130