Bank segment - Principal balance of impaired loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Recorded investment:
With no related allowance recorded	$ 15,587		$ 15,587		$ 18,811
With an allowance recorded	20,467		20,467		32,948
Recorded investment	36,054		36,054		51,759
Unpaid principal balance:
With no related allowance recorded	20,112		20,112		23,200
With an allowance recorded	20,709		20,709		33,205
Unpaid principal balance	40,821		40,821		56,405
Related Allowance	2,868		2,868		4,083
Average recorded investment:
With no related allowance recorded	14,585	$ 28,378	15,700	$ 23,365
With an allowance recorded	19,948	32,768	21,704	35,519
Average recorded investment	34,533	61,146	37,404	58,884
Interest income recognized:
With no related allowance recorded	204	228	482	484
With an allowance recorded	416	264	1,307	887
Interest income recognized	620	492	1,789	1,371
Residential 1-4 family
Recorded investment:
With no related allowance recorded	9,987		9,987		9,571
With an allowance recorded	9,770		9,770		10,283
Recorded investment	19,757		19,757		19,854
Unpaid principal balance:
With no related allowance recorded	10,541		10,541		10,400
With an allowance recorded	9,972		9,972		10,486
Unpaid principal balance	20,513		20,513		20,886
Related Allowance	1,317		1,317		1,352
Average recorded investment:
With no related allowance recorded	9,650	10,069	9,503	10,378
With an allowance recorded	9,788	11,800	9,963	11,933
Average recorded investment	19,438	21,869	19,466	22,311
Interest income recognized:
With no related allowance recorded	70	65	230	268
With an allowance recorded	97	119	333	356
Interest income recognized	167	184	563	624
Commercial real estate
Recorded investment:
With no related allowance recorded	0		0		223
With an allowance recorded	1,281		1,281		1,346
Recorded investment	1,281		1,281		1,569
Unpaid principal balance:
With no related allowance recorded	0		0		228
With an allowance recorded	1,281		1,281		1,346
Unpaid principal balance	1,281		1,281		1,574
Related Allowance	72		72		80
Average recorded investment:
With no related allowance recorded	0	1,206	121	1,177
With an allowance recorded	1,284	2,444	1,292	1,939
Average recorded investment	1,284	3,650	1,413	3,116
Interest income recognized:
With no related allowance recorded	0	0	11	0
With an allowance recorded	13	0	41	0
Interest income recognized	13	0	52	0
Home equity line of credit
Recorded investment:
With no related allowance recorded	1,565		1,565		1,500
With an allowance recorded	5,513		5,513		4,658
Recorded investment	7,078		7,078		6,158
Unpaid principal balance:
With no related allowance recorded	1,889		1,889		1,900
With an allowance recorded	5,543		5,543		4,712
Unpaid principal balance	7,432		7,432		6,612
Related Allowance	409		409		215
Average recorded investment:
With no related allowance recorded	1,918	1,220	2,108	1,035
With an allowance recorded	5,076	4,165	4,670	3,470
Average recorded investment	6,994	5,385	6,778	4,505
Interest income recognized:
With no related allowance recorded	32	6	97	15
With an allowance recorded	68	36	164	91
Interest income recognized	100	42	261	106
Residential land
Recorded investment:
With no related allowance recorded	1,134		1,134		1,218
With an allowance recorded	1,251		1,251		2,411
Recorded investment	2,385		2,385		3,629
Unpaid principal balance:
With no related allowance recorded	1,425		1,425		1,803
With an allowance recorded	1,251		1,251		2,411
Unpaid principal balance	2,676		2,676		4,214
Related Allowance	373		373		789
Average recorded investment:
With no related allowance recorded	1,209	1,521	1,080	1,532
With an allowance recorded	1,251	2,915	1,620	3,090
Average recorded investment	2,460	4,436	2,700	4,622
Interest income recognized:
With no related allowance recorded	73	16	107	47
With an allowance recorded	12	44	73	165
Interest income recognized	85	60	180	212
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	2,901		2,901		6,299
With an allowance recorded	2,585		2,585		14,240
Recorded investment	5,486		5,486		20,539
Unpaid principal balance:
With no related allowance recorded	6,257		6,257		8,869
With an allowance recorded	2,595		2,595		14,240
Unpaid principal balance	8,852		8,852		23,109
Related Allowance	667		667		1,641
Average recorded investment:
With no related allowance recorded	1,808	14,352	2,888	9,240
With an allowance recorded	2,482	11,433	4,104	15,075
Average recorded investment	4,290	25,785	6,992	24,315
Interest income recognized:
With no related allowance recorded	29	141	37	154
With an allowance recorded	225	65	694	275
Interest income recognized	254	206	731	429
Consumer loans
Recorded investment:
With no related allowance recorded	0		0		0
With an allowance recorded	67		67		10
Recorded investment	67		67		10
Unpaid principal balance:
With no related allowance recorded	0		0		0
With an allowance recorded	67		67		10
Unpaid principal balance	67		67		10
Related Allowance	30		30		$ 6
Average recorded investment:
With no related allowance recorded	0	10	0	3
With an allowance recorded	67	11	55	12
Average recorded investment	67	21	55	15
Interest income recognized:
With no related allowance recorded	0	0	0	0
With an allowance recorded	1	0	2	0
Interest income recognized	$ 1	$ 0	$ 2	$ 0