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Property and equipment (Details) - USD ($) | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Feb. 28, 2018 | Jul. 31, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Jan. 31, 2017
Property and equipment |  |  |  |  |  |  |  |  |  |
Total property and equipment, gross |  |  | $ 2,263,000 |  | $ 2,263,000 |  | $ 6,813,000 | $ 9,000,000 |  |
Less: accumulated depreciation and amortization |  |  | (1,860,000) |  | (1,860,000) |  | (3,700,000) | (3,428,000) |  |
Total property and equipment, net |  |  | 403,000 |  | 403,000 |  | 3,113,000 | 5,572,000 |  |
Depreciation and amortization expense |  |  | 200,000 | $ 500,000 | 506,000 | $ 951,000 | 1,650,000 | 2,238,000 | $ 1,286,000 |
Fixed assets held-for-sale | $ 300,000 |  |  |  |  |  | 300,000 |  |  | $ 500,000
Carrying value of assets sold |  | $ 200,000 |  |  |  |  |  |  |  |
Proceeds from sale of property held-for-sale | $ 200,000 | 300,000 |  |  |  |  |  |  |  |
Loss on sale of property, plant and equipment |  | $ 100,000 |  |  | 34,000 | $ 0 | 100,000 |  |  |
Tangible asset impairment charges |  |  |  |  | 2,200,000 |  | 400,000 | 2,000,000 | $ 0 |
Assets held-for-sale, not part of disposal group |  |  | 100,000 |  | 100,000 |  |  |  |  |
Laboratory equipment |  |  |  |  |  |  |  |  |  |
Property and equipment |  |  |  |  |  |  |  |  |  |
Total property and equipment, gross |  |  | 1,732,000 |  | 1,732,000 |  | 3,480,000 | 5,184,000 |  |
Furniture |  |  |  |  |  |  |  |  |  |
Property and equipment |  |  |  |  |  |  |  |  |  |
Total property and equipment, gross |  |  | 230,000 |  | 230,000 |  | 371,000 | 793,000 |  |
Computer equipment |  |  |  |  |  |  |  |  |  |
Property and equipment |  |  |  |  |  |  |  |  |  |
Total property and equipment, gross |  |  | 13,000 |  | 13,000 |  | 208,000 | 208,000 |  |
Leasehold improvements |  |  |  |  |  |  |  |  |  |
Property and equipment |  |  |  |  |  |  |  |  |  |
Total property and equipment, gross |  |  | $ 288,000 |  | $ 288,000 |  | $ 2,754,000 | $ 2,815,000 |  |

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- Definition Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.14) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of assets held-for-sale that are not part of a disposal group. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 15 -Paragraph 4 -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=77912953&loc=d3e400-110220 + Details
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