Fair value measurements - Summary of Level 3 financial instruments (Details) - Level 3 - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Fair value measurements
Fair value	$ 545	$ 2,621
Fair value of collateral \| Residential loan
Fair value measurements
Fair value	$ 545	$ 613
Appraised value, selling cost	7.00%	7.00%
Appraised value, weighted average rate	84.00%	84.00%
Fair value of collateral \| Residential loan \| Minimum
Fair value measurements
Appraised value	69.00%	71.00%
Fair value of collateral \| Residential loan \| Maximum
Fair value measurements
Appraised value	95.00%	92.00%
Fair value of collateral \| Commercial loans
Fair value measurements
Fair value		$ 2,008
Appraised value, weighted average rate		75.00%
Fair value of collateral \| Commercial loans \| Minimum
Fair value measurements
Appraised value		71.00%
Fair value of collateral \| Commercial loans \| Maximum
Fair value measurements
Appraised value		76.00%

Fair Value Assumptions, Appraised Value, Weighted Average Rate

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- Definition

Fair Value Assumptions, Selling Cost, Percent

+ References

No definition available.

+ Details

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- Definition

Represents the appraised value used as an input to measure fair value, expressed as a percentage.

+ References

No definition available.

+ Details

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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