Bank segment - Principal balance of impaired loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Recorded investment:
With no related allowance recorded	$ 20,028		$ 20,028		$ 16,349
With an allowance recorded	23,436		23,436		23,348
Recorded investment	43,464		43,464		39,697
Unpaid principal balance:
With no related allowance recorded	26,138		26,138		18,372
With an allowance recorded	23,519		23,519		23,580
Unpaid principal balance	49,657		49,657		41,952
Related Allowance	2,822		2,822		2,222
Average recorded investment:
With no related allowance recorded	18,397	$ 16,895	17,610	$ 15,357
With an allowance recorded	29,395	23,746	29,240	21,916
Average recorded investment	47,792	40,641	46,850	37,273
Interest income recognized:
With no related allowance recorded	470	274	833	473
With an allowance recorded	288	235	826	694
Interest income recognized	758	509	1,659	1,167
Residential 1-4 family
Recorded investment:
With no related allowance recorded	8,277		8,277		7,822
With an allowance recorded	8,279		8,279		8,672
Recorded investment	16,556		16,556		16,494
Unpaid principal balance:
With no related allowance recorded	8,877		8,877		8,333
With an allowance recorded	8,332		8,332		8,875
Unpaid principal balance	17,209		17,209		17,208
Related Allowance	906		906		876
Average recorded investment:
With no related allowance recorded	8,562	8,940	8,515	8,779
With an allowance recorded	8,296	8,820	8,377	8,909
Average recorded investment	16,858	17,760	16,892	17,688
Interest income recognized:
With no related allowance recorded	175	239	422	396
With an allowance recorded	86	84	265	274
Interest income recognized	261	323	687	670
Commercial real estate
Recorded investment:
With no related allowance recorded	0		0		0
With an allowance recorded	877		877		915
Recorded investment	877		877		915
Unpaid principal balance:
With no related allowance recorded	0		0		0
With an allowance recorded	877		877		915
Unpaid principal balance	877		877		915
Related Allowance	7		7		7
Average recorded investment:
With no related allowance recorded	0	0	0	0
With an allowance recorded	881	985	894	997
Average recorded investment	881	985	894	997
Interest income recognized:
With no related allowance recorded	0	0	0	0
With an allowance recorded	9	11	28	32
Interest income recognized	9	11	28	32
Home equity line of credit
Recorded investment:
With no related allowance recorded	1,806		1,806		2,743
With an allowance recorded	11,103		11,103		12,057
Recorded investment	12,909		12,909		14,800
Unpaid principal balance:
With no related allowance recorded	1,967		1,967		3,004
With an allowance recorded	11,133		11,133		12,086
Unpaid principal balance	13,100		13,100		15,090
Related Allowance	500		500		701
Average recorded investment:
With no related allowance recorded	1,797	2,234	2,091	2,103
With an allowance recorded	11,332	12,090	11,606	10,083
Average recorded investment	13,129	14,324	13,697	12,186
Interest income recognized:
With no related allowance recorded	12	23	78	35
With an allowance recorded	143	111	425	288
Interest income recognized	155	134	503	323
Residential land
Recorded investment:
With no related allowance recorded	3,194		3,194		2,030
With an allowance recorded	0		0		29
Recorded investment	3,194		3,194		2,059
Unpaid principal balance:
With no related allowance recorded	3,398		3,398		2,228
With an allowance recorded	0		0		29
Unpaid principal balance	3,398		3,398		2,257
Related Allowance	0		0		6
Average recorded investment:
With no related allowance recorded	3,205	1,773	2,507	1,358
With an allowance recorded	0	20	36	45
Average recorded investment	3,205	1,793	2,543	1,403
Interest income recognized:
With no related allowance recorded	40	6	90	16
With an allowance recorded	0	0	0	3
Interest income recognized	40	6	90	19
Commercial construction
Recorded investment:
With no related allowance recorded	0		0		0
With an allowance recorded	0		0		0
Recorded investment	0		0		0
Unpaid principal balance:
With no related allowance recorded	0		0		0
With an allowance recorded	0		0		0
Unpaid principal balance	0		0		0
Related Allowance	0		0		0
Average recorded investment:
With no related allowance recorded	0	0	0	0
With an allowance recorded	0	0	0	0
Average recorded investment	0	0	0	0
Interest income recognized:
With no related allowance recorded	0	0	0	0
With an allowance recorded	0	0	0	0
Interest income recognized	0	0	0	0
Residential construction
Recorded investment:
With no related allowance recorded	0		0		0
With an allowance recorded	0		0		0
Recorded investment	0		0		0
Unpaid principal balance:
With no related allowance recorded	0		0		0
With an allowance recorded	0		0		0
Unpaid principal balance	0		0		0
Related Allowance	0		0		0
Average recorded investment:
With no related allowance recorded	0	0	0	0
With an allowance recorded	0	0	0	0
Average recorded investment	0	0	0	0
Interest income recognized:
With no related allowance recorded	0	0	0	0
With an allowance recorded	0	0	0	0
Interest income recognized	0	0	0	0
Commercial loans
Recorded investment:
With no related allowance recorded	6,749		6,749		3,722
With an allowance recorded	2,621		2,621		1,618
Recorded investment	9,370		9,370		5,340
Unpaid principal balance:
With no related allowance recorded	11,894		11,894		4,775
With an allowance recorded	2,621		2,621		1,618
Unpaid principal balance	14,515		14,515		6,393
Related Allowance	905		905		628
Average recorded investment:
With no related allowance recorded	4,812	3,915	4,470	3,099
With an allowance recorded	8,330	1,774	8,026	1,824
Average recorded investment	13,142	5,689	12,496	4,923
Interest income recognized:
With no related allowance recorded	239	6	239	26
With an allowance recorded	38	28	94	94
Interest income recognized	277	34	333	120
Consumer loans
Recorded investment:
With no related allowance recorded	2		2		32
With an allowance recorded	556		556		57
Recorded investment	558		558		89
Unpaid principal balance:
With no related allowance recorded	2		2		32
With an allowance recorded	556		556		57
Unpaid principal balance	558		558		89
Related Allowance	504		504		$ 4
Average recorded investment:
With no related allowance recorded	21	33	27	18
With an allowance recorded	556	57	301	58
Average recorded investment	577	90	328	76
Interest income recognized:
With no related allowance recorded	4	0	4	0
With an allowance recorded	12	1	14	3
Interest income recognized	$ 16	$ 1	$ 18	$ 3