Bank segment - Principal balance of impaired loans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Recorded investment:
With no related allowance recorded	$ 13,999		$ 14,072
With an allowance recorded	20,632		19,321
Recorded investment	34,631		33,393
Unpaid principal balance:
With no related allowance recorded	16,034		16,041
With an allowance recorded	20,879		19,574
Unpaid principal balance	36,913		35,615
Related Allowance	2,706		2,730
Average recorded investment:
With no related allowance recorded	13,728	$ 17,643
With an allowance recorded	19,970	25,284
Average recorded investment	33,698	42,927
Interest income recognized:
With no related allowance recorded	127	130
With an allowance recorded	224	620
Interest income recognized	351	750
Residential 1-4 family
Recorded investment:
With no related allowance recorded	8,673		9,097
With an allowance recorded	9,055		9,187
Recorded investment	17,728		18,284
Unpaid principal balance:
With no related allowance recorded	9,205		9,644
With an allowance recorded	9,258		9,390
Unpaid principal balance	18,463		19,034
Related Allowance	1,207		1,248
Average recorded investment:
With no related allowance recorded	8,496	9,555
With an allowance recorded	9,129	10,048
Average recorded investment	17,625	19,603
Interest income recognized:
With no related allowance recorded	107	84
With an allowance recorded	93	119
Interest income recognized	200	203
Commercial real estate
Recorded investment:
With no related allowance recorded	0		0
With an allowance recorded	1,004		1,016
Recorded investment	1,004		1,016
Unpaid principal balance:
With no related allowance recorded	0		0
With an allowance recorded	1,004		1,016
Unpaid principal balance	1,004		1,016
Related Allowance	68		65
Average recorded investment:
With no related allowance recorded	0	220
With an allowance recorded	1,008	1,300
Average recorded investment	1,008	1,520
Interest income recognized:
With no related allowance recorded	0	0
With an allowance recorded	11	14
Interest income recognized	11	14
Home equity line of credit
Recorded investment:
With no related allowance recorded	1,690		1,496
With an allowance recorded	8,575		6,692
Recorded investment	10,265		8,188
Unpaid principal balance:
With no related allowance recorded	1,982		1,789
With an allowance recorded	8,619		6,736
Unpaid principal balance	10,601		8,525
Related Allowance	892		647
Average recorded investment:
With no related allowance recorded	1,700	2,004
With an allowance recorded	7,741	4,562
Average recorded investment	9,441	6,566
Interest income recognized:
With no related allowance recorded	5	14
With an allowance recorded	81	49
Interest income recognized	86	63
Residential land
Recorded investment:
With no related allowance recorded	1,130		1,143
With an allowance recorded	54		122
Recorded investment	1,184		1,265
Unpaid principal balance:
With no related allowance recorded	1,429		1,434
With an allowance recorded	54		122
Unpaid principal balance	1,483		1,556
Related Allowance	17		47
Average recorded investment:
With no related allowance recorded	1,168	957
With an allowance recorded	77	2,076
Average recorded investment	1,245	3,033
Interest income recognized:
With no related allowance recorded	5	26
With an allowance recorded	2	37
Interest income recognized	7	63
Commercial construction
Recorded investment:
With no related allowance recorded	0		0
With an allowance recorded	0		0
Recorded investment	0		0
Unpaid principal balance:
With no related allowance recorded	0		0
With an allowance recorded	0		0
Unpaid principal balance	0		0
Related Allowance	0		0
Average recorded investment:
With no related allowance recorded	0	0
With an allowance recorded	0	0
Average recorded investment	0	0
Interest income recognized:
With no related allowance recorded	0	0
With an allowance recorded	0	0
Interest income recognized	0	0
Residential construction
Recorded investment:
With no related allowance recorded	0		0
With an allowance recorded	0		0
Recorded investment	0		0
Unpaid principal balance:
With no related allowance recorded	0		0
With an allowance recorded	0		0
Unpaid principal balance	0		0
Related Allowance	0		0
Average recorded investment:
With no related allowance recorded	0	0
With an allowance recorded	0	0
Average recorded investment	0	0
Interest income recognized:
With no related allowance recorded	0	0
With an allowance recorded	0	0
Interest income recognized	0	0
Commercial loans
Recorded investment:
With no related allowance recorded	2,499		2,328
With an allowance recorded	1,886		2,246
Recorded investment	4,385		4,574
Unpaid principal balance:
With no related allowance recorded	3,411		3,166
With an allowance recorded	1,886		2,252
Unpaid principal balance	5,297		5,418
Related Allowance	519		694
Average recorded investment:
With no related allowance recorded	2,357	4,907
With an allowance recorded	1,957	7,268
Average recorded investment	4,314	12,175
Interest income recognized:
With no related allowance recorded	10	6
With an allowance recorded	36	401
Interest income recognized	46	407
Consumer loans
Recorded investment:
With no related allowance recorded	7		8
With an allowance recorded	58		58
Recorded investment	65		66
Unpaid principal balance:
With no related allowance recorded	7		8
With an allowance recorded	58		58
Unpaid principal balance	65		66
Related Allowance	3		$ 29
Average recorded investment:
With no related allowance recorded	7	0
With an allowance recorded	58	30
Average recorded investment	65	30
Interest income recognized:
With no related allowance recorded	0	0
With an allowance recorded	1	0
Interest income recognized	$ 1	$ 0