Balance Sheet Account Detail (Held to Maturity Marketable Securities) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2016 USD ($) security	Dec. 31, 2015 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 38,974	$ 52,768
Gross Unrealized Gain	10	1
Gross Unrealized Loss	(17)	(53)
Fair Value	$ 38,967	52,716
Average maturity	5 months
Agency bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 10,484	8,000
Gross Unrealized Gain	5	0
Gross Unrealized Loss	0	(20)
Fair Value	10,489	7,980
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	10,521	40,824
Gross Unrealized Gain	0	1
Gross Unrealized Loss	(17)	(33)
Fair Value	10,504	40,792
Commercial paper
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,977	3,944
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	3,977	$ 3,944
Government securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	13,992
Gross Unrealized Gain	5
Gross Unrealized Loss	0
Fair Value	13,997
Corporate debt securities
Schedule of Held-to-maturity Securities [Line Items]
Gross Unrealized Loss	(17)
Fair Value	$ 10,500
Held-to-maturity debt securities held | security	5
Time held in unrealized loss position	2 months