Marketable Securities, Available-for-sale (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Marketable Securities, Available-for-sale
Gain from marketable securities, net	$ 561	$ 519	$ 1,266	$ 965
Schedule of fair values of available-for-sale marketable securities
AMORTIZED COST	362,915		362,915		387,477
GROSS UNREALIZED GAINS	603		603		1,278
GROSS UNREALIZED LOSSES	(1,324)		(1,324)		(735)
ESTIMATED FAIR VALUE	362,194		362,194		388,020
Total debt securities
Schedule of fair values of available-for-sale marketable securities
AMORTIZED COST	295,051		295,051		350,350
GROSS UNREALIZED GAINS	603		603		1,278
GROSS UNREALIZED LOSSES	(1,305)		(1,305)		(728)
ESTIMATED FAIR VALUE	294,349		294,349		350,900
U.S. Treasury securities
Schedule of fair values of available-for-sale marketable securities
AMORTIZED COST	42,689		42,689		3,098
GROSS UNREALIZED GAINS	1		1		1
GROSS UNREALIZED LOSSES	(26)		(26)		0
ESTIMATED FAIR VALUE	42,664		42,664		3,099
Obligations of U.S. and local government agencies
Schedule of fair values of available-for-sale marketable securities
AMORTIZED COST	65,265		65,265		154,774
GROSS UNREALIZED GAINS	492		492		1,008
GROSS UNREALIZED LOSSES	(752)		(752)		(489)
ESTIMATED FAIR VALUE	65,005		65,005		155,293
Corporate debt securities
Schedule of fair values of available-for-sale marketable securities
AMORTIZED COST	158,846		158,846		165,153
GROSS UNREALIZED GAINS	29		29		116
GROSS UNREALIZED LOSSES	(235)		(235)		(75)
ESTIMATED FAIR VALUE	158,640		158,640		165,194
Asset-backed securities
Schedule of fair values of available-for-sale marketable securities
AMORTIZED COST	28,251		28,251		27,325
GROSS UNREALIZED GAINS	81		81		153
GROSS UNREALIZED LOSSES	(292)		(292)		(164)
ESTIMATED FAIR VALUE	28,040		28,040		27,314
Short-term pooled investments
Schedule of fair values of available-for-sale marketable securities
AMORTIZED COST	67,864		67,864		37,127
GROSS UNREALIZED GAINS	0		0		0
GROSS UNREALIZED LOSSES	(19)		(19)		(7)
ESTIMATED FAIR VALUE	$ 67,845		$ 67,845		$ 37,120

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15E

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details