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Commitments and contingencies Textual (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016 | Dec. 31, 2016
Other Commitments [Line Items] |  |  |  |  |
Operating Leases, Rent Expense | $ 2,100 | $ 2,100 | $ 6,300 | $ 6,400 |
Cash Reserve Deposit Required and Made | $ 6,700 |  | $ 6,700 |  | $ 31,800
Minimum [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Operating Leases, Lease Renewal Period Option |  |  | 4 months |  |
Maximum [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Operating Leases, Lease Renewal Period Option |  |  | 10 years |  |

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- Definition Cash deposited in a special reserve account for the exclusive benefit of customers pursuant to SEC Regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 305 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6478312&loc=d3e61473-112792 + Details
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