Financial Instruments Available-for-sale Securities (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 15,050	$ 239,113
Gross Unrealized Gains	364	434
Gross Unrealized Losses	0	(159)
Fair Value	(15,414)us-gaap_AvailableForSaleSecurities	(239,388)us-gaap_AvailableForSaleSecurities
Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss), Net of Tax	233	176
Available-for-sale Securities, Income Tax Expense on Change in Unrealized Holding Gain (Loss)	131	99
Proceeds from Sale and Maturity of Available-for-sale Securities	342,045	7,770
Gross realized gains	1,311	20
Gross realized losses	(99)	(39)
Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost		108,300
Gross Unrealized Gains		340
Gross Unrealized Losses		(69)
Fair Value		(108,571)
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost		106,335
Gross Unrealized Gains		60
Gross Unrealized Losses		(79)
Fair Value		(106,316)
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost		24,478
Gross Unrealized Gains		34
Gross Unrealized Losses		(11)
Fair Value		(24,501)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	15,050
Gross Unrealized Gains	364
Gross Unrealized Losses	0
Fair Value	$ (15,414)

Accumulated appreciation or loss, net of tax, in value of the total of available-for-sale securities at the end of an accounting period.

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Tax related to the accumulated appreciation or loss in value of the total of available-for-sale securities at the end of an accounting period.

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