Fair Value Of Financial Instruments (Fair Value Of Financial Assets Measured On A Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
ASSETS
Total assets measured at fair value	$ 41,648	$ 16,032
Cash And Cash Equivalents [Member] | Money Market Funds [Member]
ASSETS
Total cash and cash equivalents	32,030	1,726
Investments [Member] | Commercial Paper [Member]
ASSETS
Total investments	3,339
Investments [Member] | Corporate Bonds [Member]
ASSETS
Total investments	5,779	13,289
Investments [Member] | Asset-Backed Securities [Member]
ASSETS
Total investments	500	1,017
Level 1 [Member]
ASSETS
Total assets measured at fair value	32,030	1,726
Level 1 [Member] | Cash And Cash Equivalents [Member] | Money Market Funds [Member]
ASSETS
Total cash and cash equivalents	32,030	1,726
Level 2 [Member]
ASSETS
Total assets measured at fair value	9,618	14,306
Level 2 [Member] | Investments [Member] | Commercial Paper [Member]
ASSETS
Total investments	3,339
Level 2 [Member] | Investments [Member] | Corporate Bonds [Member]
ASSETS
Total investments	5,779	13,289
Level 2 [Member] | Investments [Member] | Asset-Backed Securities [Member]
ASSETS
Total investments	$ 500	$ 1,017