Financial Instruments (Available-for-sale Securities) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cost					$ 576,021
Gross Unrealized Gains					525
Gross Unrealized Losses					(8,321)
Fair Value					568,225
Net unrealized gains (losses) on available-for-sale securities					(4,995)
Proceeds from sales and maturities of securities	$ 360,506	$ 1,019	$ 662,938	$ 16,056
Gross realized gains	52,414	0	53,755	3,795
Gross realized losses	$ 13	$ 0	$ 35	$ 0
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost					54,371
Gross Unrealized Gains					466
Gross Unrealized Losses					(6,756)
Fair Value					48,081
Corporate bond securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost					336,665
Gross Unrealized Gains					55
Gross Unrealized Losses					(1,076)
Fair Value					335,644
US government debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost					135,226
Gross Unrealized Gains					2
Gross Unrealized Losses					(374)
Fair Value					134,854
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost					49,759
Gross Unrealized Gains					2
Gross Unrealized Losses					(115)
Fair Value					49,646
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Net of income tax expense (benefit) on available for sales securities					$ (2,801)