Bank segment - Principal balance of impaired loans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Recorded investment:
With no related allowance recorded	$ 18,519		$ 16,349
With an allowance recorded	31,880		23,348
Recorded investment	50,399		39,697
Unpaid principal balance:
With no related allowance recorded	20,774		18,372
With an allowance recorded	31,972		23,580
Unpaid principal balance	52,746		41,952
Related Allowance	4,242		2,222
Average recorded investment:
With no related allowance recorded	16,565	$ 13,728
With an allowance recorded	25,959	19,970
Average recorded investment	42,524	33,698
Interest income recognized:
With no related allowance recorded	198	127
With an allowance recorded	250	224
Interest income recognized	448	351
Residential 1-4 family
Recorded investment:
With no related allowance recorded	9,208		7,822
With an allowance recorded	8,195		8,672
Recorded investment	17,403		16,494
Unpaid principal balance:
With no related allowance recorded	9,833		8,333
With an allowance recorded	8,248		8,875
Unpaid principal balance	18,081		17,208
Related Allowance	771		876
Average recorded investment:
With no related allowance recorded	7,991	8,496
With an allowance recorded	8,394	9,129
Average recorded investment	16,385	17,625
Interest income recognized:
With no related allowance recorded	160	107
With an allowance recorded	83	93
Interest income recognized	243	200
Commercial real estate
Recorded investment:
With no related allowance recorded	0		0
With an allowance recorded	902		915
Recorded investment	902		915
Unpaid principal balance:
With no related allowance recorded	0		0
With an allowance recorded	902		915
Unpaid principal balance	902		915
Related Allowance	7		7
Average recorded investment:
With no related allowance recorded	0	0
With an allowance recorded	906	1,008
Average recorded investment	906	1,008
Interest income recognized:
With no related allowance recorded	0	0
With an allowance recorded	10	11
Interest income recognized	10	11
Home equity line of credit
Recorded investment:
With no related allowance recorded	2,508		2,743
With an allowance recorded	11,538		12,057
Recorded investment	14,046		14,800
Unpaid principal balance:
With no related allowance recorded	2,778		3,004
With an allowance recorded	11,577		12,086
Unpaid principal balance	14,355		15,090
Related Allowance	491		701
Average recorded investment:
With no related allowance recorded	2,534	1,700
With an allowance recorded	11,823	7,741
Average recorded investment	14,357	9,441
Interest income recognized:
With no related allowance recorded	12	5
With an allowance recorded	130	81
Interest income recognized	142	86
Residential land
Recorded investment:
With no related allowance recorded	2,036		2,030
With an allowance recorded	29		29
Recorded investment	2,065		2,059
Unpaid principal balance:
With no related allowance recorded	2,235		2,228
With an allowance recorded	29		29
Unpaid principal balance	2,264		2,257
Related Allowance	4		6
Average recorded investment:
With no related allowance recorded	2,036	1,168
With an allowance recorded	29	77
Average recorded investment	2,065	1,245
Interest income recognized:
With no related allowance recorded	26	5
With an allowance recorded	0	2
Interest income recognized	26	7
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	4,736		3,722
With an allowance recorded	11,159		1,618
Recorded investment	15,895		5,340
Unpaid principal balance:
With no related allowance recorded	5,897		4,775
With an allowance recorded	11,159		1,618
Unpaid principal balance	17,056		6,393
Related Allowance	2,965		628
Average recorded investment:
With no related allowance recorded	3,973	2,357
With an allowance recorded	4,750	1,957
Average recorded investment	8,723	4,314
Interest income recognized:
With no related allowance recorded	0	10
With an allowance recorded	26	36
Interest income recognized	26	46
Consumer loans
Recorded investment:
With no related allowance recorded	31		32
With an allowance recorded	57		57
Recorded investment	88		89
Unpaid principal balance:
With no related allowance recorded	31		32
With an allowance recorded	57		57
Unpaid principal balance	88		89
Related Allowance	4		$ 4
Average recorded investment:
With no related allowance recorded	31	7
With an allowance recorded	57	58
Average recorded investment	88	65
Interest income recognized:
With no related allowance recorded	0	0
With an allowance recorded	1	1
Interest income recognized	$ 1	$ 1