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Marketable Securities (Tables) | 3 Months Ended
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Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract] |
Schedule of Marketable Securities | At March 31, 2018, marketable securities consisted of the following (in thousands):
| Amortized Cost |  | Unrealized Gains |  | Unrealized Losses |  | Aggregate Fair Value
U.S. treasury debt securities | $ | 3,088 |  | $ | — |  | $ | (8) |  | $ | 3,080
U.S. corporate debt securities | 12,827 |  | — |  | (106) |  | 12,721
Money market funds | 54,830 |  | — |  | — |  | 54,830
| $ | 70,745 |  | $ | — |  | $ | (114) |  | $ | 70,631
Included in cash and cash equivalents | $ | 54,830 |  | $ | — |  | $ | — |  | $ | 54,830
Included in marketable securities | $ | 15,915 |  | $ | — |  | $ | (114) |  | $ | 15,801
At December 31, 2017, marketable securities consisted of the following (in thousands):
| Amortized Cost |  | Unrealized Gains |  | Unrealized Losses |  | Aggregate Fair Value
U.S. treasury debt securities | $ | 3,083 |  | $ | — |  | $ | (8) |  | $ | 3,075
U.S. corporate debt securities | 13,350 |  | — |  | (61) |  | 13,289
Money market funds | 49,452 |  | — |  | — |  | 49,452
| $ | 65,885 |  | $ | — |  | $ | (69) |  | $ | 65,816
Included in cash and cash equivalents | $ | 49,452 |  | $ | — |  | $ | — |  | $ | 49,452
Included in marketable securities | $ | 16,433 |  | $ | — |  | $ | (69) |  | $ | 16,364
Schedule of Cash and Cash Equivalents | At March 31, 2018, marketable securities consisted of the following (in thousands):
| Amortized Cost |  | Unrealized Gains |  | Unrealized Losses |  | Aggregate Fair Value
U.S. treasury debt securities | $ | 3,088 |  | $ | — |  | $ | (8) |  | $ | 3,080
U.S. corporate debt securities | 12,827 |  | — |  | (106) |  | 12,721
Money market funds | 54,830 |  | — |  | — |  | 54,830
| $ | 70,745 |  | $ | — |  | $ | (114) |  | $ | 70,631
Included in cash and cash equivalents | $ | 54,830 |  | $ | — |  | $ | — |  | $ | 54,830
Included in marketable securities | $ | 15,915 |  | $ | — |  | $ | (114) |  | $ | 15,801
At December 31, 2017, marketable securities consisted of the following (in thousands):
| Amortized Cost |  | Unrealized Gains |  | Unrealized Losses |  | Aggregate Fair Value
U.S. treasury debt securities | $ | 3,083 |  | $ | — |  | $ | (8) |  | $ | 3,075
U.S. corporate debt securities | 13,350 |  | — |  | (61) |  | 13,289
Money market funds | 49,452 |  | — |  | — |  | 49,452
| $ | 65,885 |  | $ | — |  | $ | (69) |  | $ | 65,816
Included in cash and cash equivalents | $ | 49,452 |  | $ | — |  | $ | — |  | $ | 49,452
Included in marketable securities | $ | 16,433 |  | $ | — |  | $ | (69) |  | $ | 16,364
Schedule of Available-for-sale Securities, Continuous Unrealized Loss Position | The following table presents gross unrealized losses and fair values for those marketable securities that were in an unrealized loss position as of March 31, 2018, aggregated by investment category and the length of time that individual securities have been in a continuous loss position (in thousands):
| As of March 31, 2018
| Less than 12 months |  | 12 months or greater
| Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss
U.S. treasury debt securities | $ | 1,980 |  | $ | (7) |  | $ | 1,100 |  | $ | (1)
U.S. corporate debt securities | 12,222 |  | (106) |  | — |  | —
Total | $ | 14,202 |  | $ | (113) |  | $ | 1,100 |  | $ | (1)

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- Definition Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62557-112803 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27198-111563 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62586-112803 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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