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Summary of Significant Accounting Policies - Additional Information (Narrative) (Details) - USD ($) | 6 Months Ended |
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Jun. 30, 2018 | Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items] |  |
Noncontrolling Interest, Ownership Percentage by Parent | 83.68% |
Non-controlling interest | $ 349,000 | $ 361,000
Minimum [Member] |  |
Summary Of Significant Accounting Policies [Line Items] |  |
Number of business days for related transactions | 1 day |
Maximum [Member] |  |
Summary Of Significant Accounting Policies [Line Items] |  |
Number of business days for related transactions | 2 days |

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- Definition Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (that is, noncontrolling interest, previously referred to as minority interest). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(22)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(24)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.31) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Percentage of subsidiary's or equity method investee's stock owned by parent immediately after all stock transactions. + References No definition available. + Details
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