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Significant Accounting Policies Stock-based compensation (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended | 76 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Apr. 30, 2018
Significant Accounting Policies [Abstract] |  |  |  |
Stock-based Compensation | $ 1,134 us-gaap_ShareBasedCompensation | $ 1,184 us-gaap_ShareBasedCompensation | $ 2,379 us-gaap_ShareBasedCompensation | $ 6,500 us-gaap_ShareBasedCompensation

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- Details
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- Definition The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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