Cash, Cash Equivalents, And Available-For-Sale Securities (Fair Value Hierarchy for Cash Equivalents and Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair value measurements
Cash and Cash Equivalents, Fair Value Disclosure	$ 23,021	$ 30,411
Debt Securities, Available-for-sale, Current	81,632	80,838
Cash and cash equivalents and available for sale securities, Fair Value Disclosure	104,653	111,249
U.S. Treasury securities
Fair value measurements
Debt Securities, Available-for-sale, Current	38,996	42,184
Corporate Debt Securities
Fair value measurements
Debt Securities, Available-for-sale, Current	42,636	38,654
Level 1
Fair value measurements
Cash and Cash Equivalents, Fair Value Disclosure	23,021	30,411
Cash and cash equivalents and available for sale securities, Fair Value Disclosure	62,017	72,595
Level 1 \| U.S. Treasury securities
Fair value measurements
Debt Securities, Available-for-sale, Current	38,996	42,184
Level 2
Fair value measurements
Cash and cash equivalents and available for sale securities, Fair Value Disclosure	42,636	38,654
Level 2 \| Corporate Debt Securities
Fair value measurements
Debt Securities, Available-for-sale, Current	$ 42,636	$ 38,654

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26626-111562

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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