Bank segment - Derivatives (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Not designated as a hedging instrument
Derivative instrument
Asset derivatives	$ 282		$ 137
Liability derivatives	87		30
Net gains (losses) recognized in the Statement of Income	88	$ (31)
Interest rate lock commitments
Derivative instrument
Notional amount	24,741		13,669
Fair value	255		131
Interest rate lock commitments \| Not designated as a hedging instrument
Derivative instrument
Asset derivatives	264		133
Liability derivatives	9		2
Interest rate lock commitments \| Not designated as a hedging instrument \| Mortgage banking income
Derivative instrument
Net gains (losses) recognized in the Statement of Income	124	(104)
Forward commitments
Derivative instrument
Notional amount	26,844		14,465
Fair value	(60)		(24)
Forward commitments \| Not designated as a hedging instrument
Derivative instrument
Asset derivatives	18		4
Liability derivatives	78		$ 28
Forward commitments \| Not designated as a hedging instrument \| Mortgage banking income
Derivative instrument
Net gains (losses) recognized in the Statement of Income	$ (36)	$ 73

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Section 50
-Paragraph 8
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+ References

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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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