Balance Sheet Account Detail (Held to Maturity Marketable Securities) (Details) $ in Thousands	Jun. 30, 2015 USD ($) securities	Dec. 31, 2014 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 34,257	$ 59,871
Gross Unrealized Gain	7	5
Gross Unrealized Loss	(2)	(8)
Fair Value	34,262	59,868
Asset backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	857	3,633
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	857	3,633
Agency bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,000
Gross Unrealized Gain	0
Gross Unrealized Loss	0
Fair Value	3,000
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,658	15,707
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(1)	(8)
Fair Value	2,657	15,699
Commercial paper
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	22,781	40,531
Gross Unrealized Gain	5	5
Gross Unrealized Loss	(1)	0
Fair Value	22,785	$ 40,536
Government securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	4,961
Gross Unrealized Gain	2
Gross Unrealized Loss	0
Fair Value	4,963
Corporate debt securities
Schedule of Held-to-maturity Securities [Line Items]
Gross Unrealized Loss	(2)
Fair Value	$ 4,700
Held-to-maturity debt securities held | securities	6