Bank segment - Principal balance of impaired loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Recorded investment:
With no related allowance recorded	$ 18,447		$ 18,447		$ 16,349
With an allowance recorded	32,844		32,844		23,348
Recorded investment	51,291		51,291		39,697
Unpaid principal balance:
With no related allowance recorded	20,782		20,782		18,372
With an allowance recorded	33,035		33,035		23,580
Unpaid principal balance	53,817		53,817		41,952
Related Allowance	6,860		6,860		2,222
Average recorded investment:
With no related allowance recorded	17,870	$ 15,447	17,218	$ 14,588
With an allowance recorded	32,363	22,031	29,161	21,000
Average recorded investment	50,233	37,478	46,379	35,588
Interest income recognized:
With no related allowance recorded	165	72	363	199
With an allowance recorded	288	235	538	459
Interest income recognized	453	307	901	658
Residential 1-4 family
Recorded investment:
With no related allowance recorded	9,208		9,208		7,822
With an allowance recorded	8,329		8,329		8,672
Recorded investment	17,537		17,537		16,494
Unpaid principal balance:
With no related allowance recorded	9,833		9,833		8,333
With an allowance recorded	8,382		8,382		8,875
Unpaid principal balance	18,215		18,215		17,208
Related Allowance	904		904		876
Average recorded investment:
With no related allowance recorded	8,993	8,900	8,492	8,699
With an allowance recorded	8,440	8,778	8,417	8,953
Average recorded investment	17,433	17,678	16,909	17,652
Interest income recognized:
With no related allowance recorded	87	50	247	157
With an allowance recorded	96	97	179	190
Interest income recognized	183	147	426	347
Commercial real estate
Recorded investment:
With no related allowance recorded	0		0		0
With an allowance recorded	890		890		915
Recorded investment	890		890		915
Unpaid principal balance:
With no related allowance recorded	0		0		0
With an allowance recorded	890		890		915
Unpaid principal balance	890		890		915
Related Allowance	7		7		7
Average recorded investment:
With no related allowance recorded	0	0	0	0
With an allowance recorded	894	997	900	1,003
Average recorded investment	894	997	900	1,003
Interest income recognized:
With no related allowance recorded	0	0	0	0
With an allowance recorded	9	10	19	21
Interest income recognized	9	10	19	21
Home equity line of credit
Recorded investment:
With no related allowance recorded	1,787		1,787		2,743
With an allowance recorded	11,589		11,589		12,057
Recorded investment	13,376		13,376		14,800
Unpaid principal balance:
With no related allowance recorded	2,073		2,073		3,004
With an allowance recorded	11,623		11,623		12,086
Unpaid principal balance	13,696		13,696		15,090
Related Allowance	465		465		701
Average recorded investment:
With no related allowance recorded	1,940	2,374	2,238	2,037
With an allowance recorded	11,665	10,420	11,743	9,080
Average recorded investment	13,605	12,794	13,981	11,117
Interest income recognized:
With no related allowance recorded	54	7	66	12
With an allowance recorded	152	96	282	177
Interest income recognized	206	103	348	189
Residential land
Recorded investment:
With no related allowance recorded	2,869		2,869		2,030
With an allowance recorded	0		0		29
Recorded investment	2,869		2,869		2,059
Unpaid principal balance:
With no related allowance recorded	3,072		3,072		2,228
With an allowance recorded	0		0		29
Unpaid principal balance	3,072		3,072		2,257
Related Allowance	0		0		6
Average recorded investment:
With no related allowance recorded	2,280	1,132	2,158	1,150
With an allowance recorded	79	40	54	58
Average recorded investment	2,359	1,172	2,212	1,208
Interest income recognized:
With no related allowance recorded	24	5	50	10
With an allowance recorded	0	1	0	3
Interest income recognized	24	6	50	13
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	4,553		4,553		3,722
With an allowance recorded	11,480		11,480		1,618
Recorded investment	16,033		16,033		5,340
Unpaid principal balance:
With no related allowance recorded	5,774		5,774		4,775
With an allowance recorded	11,584		11,584		1,618
Unpaid principal balance	17,358		17,358		6,393
Related Allowance	4,983		4,983		628
Average recorded investment:
With no related allowance recorded	4,626	3,026	4,299	2,691
With an allowance recorded	10,997	1,738	7,874	1,848
Average recorded investment	15,623	4,764	12,173	4,539
Interest income recognized:
With no related allowance recorded	0	10	0	20
With an allowance recorded	30	30	56	66
Interest income recognized	30	40	56	86
Consumer loans
Recorded investment:
With no related allowance recorded	30		30		32
With an allowance recorded	556		556		57
Recorded investment	586		586		89
Unpaid principal balance:
With no related allowance recorded	30		30		32
With an allowance recorded	556		556		57
Unpaid principal balance	586		586		89
Related Allowance	501		501		$ 4
Average recorded investment:
With no related allowance recorded	31	15	31	11
With an allowance recorded	288	58	173	58
Average recorded investment	319	73	204	69
Interest income recognized:
With no related allowance recorded	0	0	0	0
With an allowance recorded	1	1	2	2
Interest income recognized	$ 1	$ 1	$ 2	$ 2