Cash, Cash Equivalents And Marketable Securities And Assets Measured At Fair Value (Cash, Cash Equivalents And Marketable Securities) (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Dec. 31, 2016 |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Cash and cash equivalents | $ 20,444 | $ 10,479 | $ 11,916 | $ 16,615 |
Cash and cash equivalents, Short Term Investment, Amortized Cost | 20,444 | 10,479 | | |
Cash and cash equivalents, Short Term Investment Unrealized Gains | | | | |
Cash and cash equivalents, Short Term Investment Unrealized Losses | | | | |
Accrued Interest | | | | |
Cash and cash equivalents, Short Term Investment, Fair Value | 20,444 | 10,479 | | |
Estimated Fair Value, Fair Value Disclosure [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Cash and cash equivalents, Short Term Investment, Fair Value | 20,444 | 10,479 | | |
Marketable Securities [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Available-for-sale securities, Amortized Cost Basis | | | | |
Available-for-sale securities, Gross Unrealized Gains | | | | |
Available-for-sale securities, Gross Unrealized Losses | | | | |
Accrued Interest | | | | |
Estimated Fair Value, Marketable securities | | | | |
Marketable Securities [Member] | Estimated Fair Value, Fair Value Disclosure [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Estimated Fair Value, Marketable securities | | | | |
Cash [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Cash | 590 | 158 | | |
Available-for-sale securities, Gross Unrealized Gains | | | | |
Available-for-sale securities, Gross Unrealized Losses | | | | |
Accrued Interest | | | | |
Cash and cash equivalents, Fair Value | 590 | 158 | | |
Cash [Member] | Estimated Fair Value, Fair Value Disclosure [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Cash and cash equivalents, Fair Value | 590 | 158 | | |
Cash Equivalents [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Cash equivalents | 19,854 | 10,321 | | |
Available-for-sale securities, Gross Unrealized Gains | | | | |
Available-for-sale securities, Gross Unrealized Losses | | | | |
Accrued Interest | | | | |
Cash and cash equivalents, Fair Value | 19,854 | 10,321 | | |
Cash Equivalents [Member] | Estimated Fair Value, Fair Value Disclosure [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Cash and cash equivalents, Fair Value | 19,854 | 10,321 | | |
Cash And Cash Equivalents [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Cash and cash equivalents | 20,444 | 10,479 | | |
Available-for-sale securities, Gross Unrealized Gains | | | | |
Available-for-sale securities, Gross Unrealized Losses | | | | |
Accrued Interest | | | | |
Cash and cash equivalents, Fair Value | 20,444 | 10,479 | | |
Cash And Cash Equivalents [Member] | Estimated Fair Value, Fair Value Disclosure [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Cash and cash equivalents, Fair Value | 20,444 | 10,479 | | |
Matures In One Year Or Less [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Cash and cash equivalents, Short Term Investment, Amortized Cost | 20,444 | 10,479 | | |
Available-for-sale securities, Gross Unrealized Gains | | | | |
Available-for-sale securities, Gross Unrealized Losses | | | | |
Accrued Interest | | | | |
Cash and cash equivalents, Short Term Investment, Fair Value | 20,444 | 10,479 | | |
Matures In One Year Or Less [Member] | Estimated Fair Value, Fair Value Disclosure [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Cash and cash equivalents, Short Term Investment, Fair Value | 20,444 | 10,479 | | |
Matures One To Three Years [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Cash and cash equivalents, Short Term Investment, Amortized Cost | | | | |
Available-for-sale securities, Gross Unrealized Gains | | | | |
Available-for-sale securities, Gross Unrealized Losses | | | | |
Accrued Interest | | | | |
Cash and cash equivalents, Short Term Investment, Fair Value | | | | |
Matures One To Three Years [Member] | Estimated Fair Value, Fair Value Disclosure [Member] | | | | |
Schedule of Available-for-sale Securities [Line Items] | | | | |
Cash and cash equivalents, Short Term Investment, Fair Value | | | | |