Fair Value Measurements (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value Measurements
Commitments, Fair Value Disclosure	$ 4,552	$ 4,477
Nonfinancial Liabilities Fair Value Disclosure	4,552	4,477
Level 1
Fair Value Measurements
Cash equivalents	175,409	192,207
Total assets	175,409	192,207
Commitments, Fair Value Disclosure	0	0
Nonfinancial Liabilities Fair Value Disclosure	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value Measurements
Cash equivalents	0	0
Commitments, Fair Value Disclosure	0	0
Nonfinancial Liabilities Fair Value Disclosure	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements
Cash equivalents	0	0
Commitments, Fair Value Disclosure	4,552	4,477
Nonfinancial Liabilities Fair Value Disclosure	4,552	4,477
Total fair value
Fair Value Measurements
Cash equivalents	175,409	192,207
Total assets	$ 175,409	$ 192,207

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

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

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- Definition

Fair value portion of arrangements with third parties, including, but not limited to, operating lease arrangement and arrangement in which the entity has agreed to expend funds to procure goods or services, or has agreed to commit resources to supply goods or services.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(25))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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

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- Definition

Fair value of obligations not classified as financial liabilities. Includes, but is not limited to, accounts payable and accrued liabilities, commitments, obligations, and other liabilities.

+ References

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