Balance Sheet Account Detail (Held to Maturity Marketable Securities) (Details) $ in Thousands	Sep. 30, 2015 USD ($) securities	Dec. 31, 2014 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 32,891	$ 59,871
Gross Unrealized Gain	10	5
Gross Unrealized Loss	(1)	(8)
Fair Value	32,900	59,868
Asset backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	193	3,633
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	193	3,633
Agency bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	4,000
Gross Unrealized Gain	0
Gross Unrealized Loss	0
Fair Value	4,000
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,703	15,707
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(1)	(8)
Fair Value	1,702	15,699
Commercial paper
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	10,094	40,531
Gross Unrealized Gain	1	5
Gross Unrealized Loss	0	0
Fair Value	10,095	$ 40,536
Government securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	16,901
Gross Unrealized Gain	9
Gross Unrealized Loss	0
Fair Value	16,910
Corporate debt securities
Schedule of Held-to-maturity Securities [Line Items]
Gross Unrealized Loss	(1)
Fair Value	$ 7,300
Held-to-maturity debt securities held | securities	5