Balance Sheet Account Detail (Held to Maturity Marketable Securities) (Details) $ in Thousands	Mar. 31, 2016 USD ($) securities	Dec. 31, 2015 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 46,441	$ 52,768
Gross Unrealized Gain	15	1
Gross Unrealized Loss	(7)	(53)
Fair Value	46,449	52,716
Agency bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	8,000	8,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(5)	(20)
Fair Value	7,995	7,980
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		40,824
Gross Unrealized Gain		1
Gross Unrealized Loss		(33)
Fair Value		40,792
Commercial paper
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,497	3,944
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	2,497	$ 3,944
Government securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	35,944
Gross Unrealized Gain	15
Gross Unrealized Loss	(2)
Fair Value	35,957
Corporate debt securities
Schedule of Held-to-maturity Securities [Line Items]
Gross Unrealized Loss	(7)
Fair Value	$ 12,000
Held-to-maturity debt securities held | securities	3