Bank segment - Loan modifications (Details) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2017 USD ($) contract	Mar. 31, 2016 USD ($) contract	Dec. 31, 2016 USD ($)
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment	$ 29,401		$ 37,637
Residential 1-4 family
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment	13,661		14,450
Commercial real estate
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment	1,297		1,346
Home equity line of credit
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment	4,894		4,934
Residential land
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment	2,246		2,751
Commercial construction
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment	0		0
Residential construction
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment	0		0
Commercial loans
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment	7,234		14,146
Consumer loans
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment	$ 69		$ 10
Troubled debt restructurings real estate loans
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) \| contract	13	17
Pre-modification outstanding recorded investment	$ 1,139	$ 17,966
Post-modification outstanding recorded investment	1,133	18,084
Net increase in allowance	$ 106	$ 760
Troubled debt restructurings real estate loans \| Residential 1-4 family
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) \| contract	3	4
Pre-modification outstanding recorded investment	$ 512	$ 1,097
Post-modification outstanding recorded investment	520	1,215
Net increase in allowance	$ 45	$ 161
Troubled debt restructurings real estate loans \| Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) \| contract	0	0
Pre-modification outstanding recorded investment	$ 0	$ 0
Post-modification outstanding recorded investment	0	0
Net increase in allowance	$ 0	$ 0
Troubled debt restructurings real estate loans \| Home equity line of credit
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) \| contract	8	10
Pre-modification outstanding recorded investment	$ 226	$ 669
Post-modification outstanding recorded investment	212	669
Net increase in allowance	$ 34	$ 74
Troubled debt restructurings real estate loans \| Residential land
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) \| contract	0	0
Pre-modification outstanding recorded investment	$ 0	$ 0
Post-modification outstanding recorded investment	0	0
Net increase in allowance	$ 0	$ 0
Troubled debt restructurings real estate loans \| Commercial construction
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) \| contract	0	0
Pre-modification outstanding recorded investment	$ 0	$ 0
Post-modification outstanding recorded investment	0	0
Net increase in allowance	$ 0	$ 0
Troubled debt restructurings real estate loans \| Residential construction
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) \| contract	0	0
Pre-modification outstanding recorded investment	$ 0	$ 0
Post-modification outstanding recorded investment	0	0
Net increase in allowance	$ 0	$ 0
Troubled debt restructurings real estate loans \| Commercial loans
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) \| contract	1	3
Pre-modification outstanding recorded investment	$ 342	$ 16,200
Post-modification outstanding recorded investment	342	16,200
Net increase in allowance	$ 0	$ 525
Troubled debt restructurings real estate loans \| Consumer loans
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) \| contract	1	0
Pre-modification outstanding recorded investment	$ 59	$ 0
Post-modification outstanding recorded investment	59	0
Net increase in allowance	$ 27	$ 0

Amount of increase (decrease) of allowance reserve for credit loss.

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 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953676-111524

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