Balance Sheet Account Detail (Held to Maturity Marketable Securities) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 18,496	$ 20,988
Gross Unrealized Gain	0	2
Gross Unrealized Loss	(12)	(21)
Fair Value	$ 18,484	20,969
Average maturity	2 months
Agency bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 3,992	6,488
Gross Unrealized Gain	0	2
Gross Unrealized Loss	(2)	0
Fair Value	3,990	6,490
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	10,506	10,513
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(10)	(21)
Fair Value	10,496	10,492
Commercial paper
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,998	3,987
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	3,998	$ 3,987
Corporate debt securities
Schedule of Held-to-maturity Securities [Line Items]
Gross Unrealized Loss	(12)
Fair Value	$ 14,500
Held-to-maturity debt securities held | security	6
Time held in unrealized loss position (less than)	8 months