Bank segment - Credit risk profile - summary (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Credit risk profile based on nonaccrual loans
Nonaccrual loans	$ 35,181	$ 36,886
Accruing loans 90 days or more past due	0	0
Financing Receivable, Modifications, Post-Modification Recorded Investment	24,906	24,107
Residential 1-4 family
Credit risk profile based on nonaccrual loans
Nonaccrual loans	18,205	19,253
Financing Receivable, Modifications, Post-Modification Recorded Investment	14,334	13,525
Commercial real estate
Credit risk profile based on nonaccrual loans
Nonaccrual loans	4,998	5,112
Financing Receivable, Modifications, Post-Modification Recorded Investment	0	0
Home equity line of credit
Credit risk profile based on nonaccrual loans
Nonaccrual loans	1,701	1,087
Financing Receivable, Modifications, Post-Modification Recorded Investment	750	480
Residential land
Credit risk profile based on nonaccrual loans
Nonaccrual loans	717	720
Accruing loans 90 days or more past due
Financing Receivable, Modifications, Post-Modification Recorded Investment	7,102	7,130
Commercial construction
Credit risk profile based on nonaccrual loans
Financing Receivable, Modifications, Post-Modification Recorded Investment	0	0
Residential construction
Credit risk profile based on nonaccrual loans
Financing Receivable, Modifications, Post-Modification Recorded Investment	0	0
Commercial loans
Credit risk profile based on nonaccrual loans
Nonaccrual loans	9,018	10,053
Accruing loans 90 days or more past due		0
Financing Receivable, Modifications, Post-Modification Recorded Investment	2,720	2,972
Consumer loans
Credit risk profile based on nonaccrual loans
Nonaccrual loans	542	661
Accruing loans 90 days or more past due		0
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 0

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

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=35738203&loc=SL6953676-111524

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- Definition

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5111-111524

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- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

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