Balance Sheet Account Detail (Held to Maturity Marketable Securities) (Details) $ in Thousands	Jun. 30, 2016 USD ($) security	Dec. 31, 2015 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 41,490	$ 52,768
Gross Unrealized Gain	12	1
Gross Unrealized Loss	(4)	(53)
Fair Value	41,498	52,716
Agency bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	10,507	8,000
Gross Unrealized Gain	2	0
Gross Unrealized Loss	(1)	(20)
Fair Value	10,508	7,980
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,510	40,824
Gross Unrealized Gain	0	1
Gross Unrealized Loss	(3)	(33)
Fair Value	2,507	40,792
Commercial paper
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,500	3,944
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	2,500	$ 3,944
Government securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	25,973
Gross Unrealized Gain	10
Gross Unrealized Loss	0
Fair Value	25,983
Corporate debt securities
Schedule of Held-to-maturity Securities [Line Items]
Gross Unrealized Loss	(4)
Fair Value	$ 10,500
Held-to-maturity debt securities held | security	3