Short-Term and Long-Term Marketable Securities (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 113,937,000	$ 28,473,000
Gross Unrealized Gains	29,000	17,000
Gross Unrealized Losses	(33,000)	(5,000)
Fair Value	113,933,000	28,485,000
Short-term Investments | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	29,054,000	18,767,000
Gross Unrealized Gains	10,000	7,000
Gross Unrealized Losses	(14,000)	(4,000)
Fair Value	29,050,000	18,770,000
Short-term Investments | U.S. dollar dominated foreign corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,824,000	5,060,000
Gross Unrealized Gains	4,000	9,000
Gross Unrealized Losses	(5,000)	(1,000)
Fair Value	12,823,000	5,068,000
Short-term Investments | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	42,436,000	4,646,000
Gross Unrealized Gains	15,000	1,000
Gross Unrealized Losses	0	0
Fair Value	42,451,000	4,647,000
Short-term Investments | Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,150,000
Gross Unrealized Gains	0
Gross Unrealized Losses	(1,000)
Fair Value	1,149,000
Short-term Investments | US Government Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	26,473,000
Gross Unrealized Gains	0
Gross Unrealized Losses	(10,000)
Fair Value	26,463,000
Short-term Investments | Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,000,000
Gross Unrealized Gains	0
Gross Unrealized Losses	(3,000)
Fair Value	1,997,000
Long-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	63,039,000	21,239,000
Gross Unrealized Gains	2,000	21,000
Gross Unrealized Losses	(156,000)	(8,000)
Fair Value	62,885,000	21,252,000
Long-term Investments | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	25,555,000	16,132,000
Gross Unrealized Gains	1,000	16,000
Gross Unrealized Losses	(81,000)	(7,000)
Fair Value	25,475,000	16,141,000
Long-term Investments | U.S. dollar dominated foreign corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,189,000	3,038,000
Gross Unrealized Gains	0	4,000
Gross Unrealized Losses	(46,000)	(1,000)
Fair Value	15,143,000	3,041,000
Long-term Investments | Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,906,000
Gross Unrealized Gains	0
Gross Unrealized Losses	(14,000)
Fair Value	8,892,000
Long-term Investments | US Government Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,768,000	2,069,000
Gross Unrealized Gains	1,000	1,000
Gross Unrealized Losses	(5,000)	0
Fair Value	7,764,000	2,070,000
Long-term Investments | Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,000,000
Gross Unrealized Gains	0
Gross Unrealized Losses	(8,000)
Fair Value	1,992,000
Long-term Investments | US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,621,000
Gross Unrealized Gains	0
Gross Unrealized Losses	(2,000)
Fair Value	$ 3,619,000