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Earnings Per Share - Additional Information (Detail) - shares |  |  | 3 Months Ended
--- | --- | --- | ---
Apr. 11, 2018 | Nov. 13, 2017 | Mar. 31, 2018 | Dec. 31, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] |  |  |  |
Anti-dilutive common stock equivalents excluded from calculation of diluted earnings per share |  |  | 1,101,513 | 1,549,440
Acquisition of ETFS Business [Member] | Series A Non-Voting Convertible Preferred Stock [Member] |  |  |  |
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] |  |  |  |
Business acquisition, number of shares to be issued |  | 14,750 |  |
Common Stock [Member] | Acquisition of ETFS Business [Member] |  |  |  |
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] |  |  |  |
Business acquisition, number of shares to be issued |  | 15,250,000 |  |
Subsequent Event [Member] | Acquisition of ETFS Business [Member] |  |  |  |
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] |  |  |  |
Business acquisition, number of shares to be issued | 30,000,000 |  |  |
Subsequent Event [Member] | Acquisition of ETFS Business [Member] | Series A Non-Voting Convertible Preferred Stock [Member] |  |  |  |
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] |  |  |  |
Business acquisition, number of shares to be issued | 14,750 |  |  |
Subsequent Event [Member] | Common Stock [Member] | Acquisition of ETFS Business [Member] |  |  |  |
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] |  |  |  |
Business acquisition, number of shares to be issued | 15,250,000 |  |  |

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- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
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- Definition Number of shares of equity interests issued or issuable to acquire entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b)(4) -URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479 + Details
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