Balance Sheet Account Detail Held to Maturity Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014 securities	Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 73,780	$ 31,313
Gross Unrealized Gain	9	3
Gross Unrealized Loss	(13)	(3)
Fair Value	73,776	31,313
Number of Securities Held	15
Asset backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5,181	1,405
Gross Unrealized Gain	1	0
Gross Unrealized Loss	0	0
Fair Value	5,182	1,405
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	20,425
Gross Unrealized Gain	2
Gross Unrealized Loss	(11)
Fair Value	20,416
Commercial paper
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	48,174	29,908
Gross Unrealized Gain	6	3
Gross Unrealized Loss	(2)	(3)
Fair Value	48,178	29,908
Corporate debt securities
Schedule of Held-to-maturity Securities [Line Items]
Gross Unrealized Loss	(13)
Fair Value	$ 73,776