Bank segment - Loan modifications (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017 USD ($) contract	Jun. 30, 2016 USD ($) contract	Jun. 30, 2017 USD ($) contract	Jun. 30, 2016 USD ($) contract	Dec. 31, 2016 USD ($)
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment			$ 23,383		$ 37,637
Residential 1-4 family
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment			13,112		14,450
Commercial real estate
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment			1,289		1,346
Home equity line of credit
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment			4,548		4,934
Residential land
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment			1,674		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			2,692		14,146
Consumer loans
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment			$ 68		$ 10
Troubled debt restructurings real estate loans
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	7	19	20	36
Pre-modification outstanding recorded investment	$ 658	$ 2,236	$ 1,797	$ 20,202
Post-modification outstanding recorded investment	658	2,231	1,791	20,315
Net increase in allowance	$ 59	$ 424	$ 165	$ 1,184
Troubled debt restructurings real estate loans | Residential 1-4 family
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	2	5	5	9
Pre-modification outstanding recorded investment	$ 360	$ 891	$ 872	$ 1,988
Post-modification outstanding recorded investment	360	885	880	2,100
Net increase in allowance	$ 0	$ 98	$ 45	$ 259
Troubled debt restructurings real estate loans | Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	0	0	0
Pre-modification outstanding recorded investment	$ 0	$ 0	$ 0	$ 0
Post-modification outstanding recorded investment	0	0	0	0
Net increase in allowance	$ 0	$ 0	$ 0	$ 0
Troubled debt restructurings real estate loans | Home equity line of credit
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	5	8	13	18
Pre-modification outstanding recorded investment	$ 298	$ 768	$ 524	$ 1,437
Post-modification outstanding recorded investment	298	768	510	1,437
Net increase in allowance	$ 59	$ 181	$ 93	$ 255
Troubled debt restructurings real estate loans | Residential land
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	1	0	1
Pre-modification outstanding recorded investment	$ 0	$ 120	$ 0	$ 120
Post-modification outstanding recorded investment	0	121	0	121
Net increase in allowance	$ 0	$ 0	$ 0	$ 0
Troubled debt restructurings real estate loans | Commercial construction
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	0	0	0
Pre-modification outstanding recorded investment	$ 0	$ 0	$ 0	$ 0
Post-modification outstanding recorded investment	0	0	0	0
Net increase in allowance	$ 0	$ 0	$ 0	$ 0
Troubled debt restructurings real estate loans | Residential construction
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	0	0	0
Pre-modification outstanding recorded investment	$ 0	$ 0	$ 0	$ 0
Post-modification outstanding recorded investment	0	0	0	0
Net increase in allowance	$ 0	$ 0	$ 0	$ 0
Troubled debt restructurings real estate loans | Commercial loans
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	5	1	8
Pre-modification outstanding recorded investment	$ 0	$ 457	$ 342	$ 16,657
Post-modification outstanding recorded investment	0	457	342	16,657
Net increase in allowance	$ 0	$ 145	$ 0	$ 670
Troubled debt restructurings real estate loans | Consumer loans
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	0	1	0
Pre-modification outstanding recorded investment	$ 0	$ 0	$ 59	$ 0
Post-modification outstanding recorded investment	0	0	59	0
Net increase in allowance	$ 0	$ 0	$ 27	$ 0