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Cash and Cash Equivalents | 12 Months Ended
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Dec. 31, 2017
Cash and Cash Equivalents |
Cash and Cash Equivalents | 4. Cash and Cash Equivalents The following is a summary of cash and cash equivalents at December 31, 2016 and 2017 (in thousands):
|  |  | December 31, |
|  |  | 2016 |  |  | 2017 |
Cash |  |  |  | $ | 5,332 |  |  |  |  | $ | 1,103 |  |
Investments with original maturity of less than three months at the time of purchase |  |  |  |  | 11,188 |  |  |  |  |  | 22,807 |  |
Total cash and cash equivalents |  |  |  | $ | 16,520 |  |  |  |  | $ | 23,910 |  |
Investments with original maturity of less than three months at time of purchase are made up of money market funds and commercial paper.

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- Definition The entire disclosure for cash and cash equivalent footnotes, which may include the types of deposits and money market instruments, applicable carrying amounts, restricted amounts and compensating balance arrangements. Cash and equivalents include: (1) currency on hand (2) demand deposits with banks or financial institutions (3) other kinds of accounts that have the general characteristics of demand deposits (4) 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. Generally, only investments maturing within three months from the date of acquisition qualify. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 305 -URI http://asc.fasb.org/topic&trid=2122426 + Details
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