Bank segment - Principal balance of impaired loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Recorded investment:
With no related allowance recorded	$ 21,020		$ 21,020		$ 19,806
With an allowance recorded	43,318		43,318		33,879
Recorded investment	64,338		64,338		53,685
Unpaid principal balance:
With no related allowance recorded	24,754		24,754		22,934
With an allowance recorded	44,035		44,035		34,696
Unpaid principal balance	68,789		68,789		57,630
Related Allowance	8,513		8,513		6,320
Average recorded investment:
With no related allowance recorded	28,378	$ 18,187	23,365	$ 20,413
With an allowance recorded	32,768	35,971	35,519	30,257
Average recorded investment	61,146	54,158	58,884	50,670
Interest income recognized:
With no related allowance recorded	228	226	484	620
With an allowance recorded	264	367	887	890
Interest income recognized	492	593	1,371	1,510
Residential 1-4 family
Recorded investment:
With no related allowance recorded	10,137		10,137		10,596
With an allowance recorded	11,429		11,429		11,861
Recorded investment	21,566		21,566		22,457
Unpaid principal balance:
With no related allowance recorded	11,473		11,473		11,805
With an allowance recorded	11,632		11,632		11,914
Unpaid principal balance	23,105		23,105		23,719
Related Allowance	1,625		1,625		1,453
Average recorded investment:
With no related allowance recorded	10,069	11,159	10,378	11,301
With an allowance recorded	11,800	11,451	11,933	11,585
Average recorded investment	21,869	22,610	22,311	22,886
Interest income recognized:
With no related allowance recorded	65	119	268	274
With an allowance recorded	119	174	356	430
Interest income recognized	184	293	624	704
Commercial real estate
Recorded investment:
With no related allowance recorded	1,351		1,351		1,188
With an allowance recorded	2,411		2,411		0
Recorded investment	3,762		3,762		1,188
Unpaid principal balance:
With no related allowance recorded	1,645		1,645		1,436
With an allowance recorded	2,482		2,482		0
Unpaid principal balance	4,127		4,127		1,436
Related Allowance	161		161		0
Average recorded investment:
With no related allowance recorded	1,206	0	1,177	362
With an allowance recorded	2,444	0	1,939	1,985
Average recorded investment	3,650	0	3,116	2,347
Interest income recognized:
With no related allowance recorded	0	74	0	74
With an allowance recorded	0	0	0	0
Interest income recognized	0	74	0	74
Home equity line of credit
Recorded investment:
With no related allowance recorded	1,300		1,300		707
With an allowance recorded	4,587		4,587		2,518
Recorded investment	5,887		5,887		3,225
Unpaid principal balance:
With no related allowance recorded	1,695		1,695		948
With an allowance recorded	4,657		4,657		2,579
Unpaid principal balance	6,352		6,352		3,527
Related Allowance	1,040		1,040		442
Average recorded investment:
With no related allowance recorded	1,220	498	1,035	444
With an allowance recorded	4,165	2,048	3,470	1,295
Average recorded investment	5,385	2,546	4,505	1,739
Interest income recognized:
With no related allowance recorded	6	1	15	3
With an allowance recorded	36	13	91	27
Interest income recognized	42	14	106	30
Residential land
Recorded investment:
With no related allowance recorded	1,608		1,608		1,644
With an allowance recorded	2,819		2,819		4,039
Recorded investment	4,427		4,427		5,683
Unpaid principal balance:
With no related allowance recorded	2,304		2,304		2,412
With an allowance recorded	2,819		2,819		4,117
Unpaid principal balance	5,123		5,123		6,529
Related Allowance	951		951		891
Average recorded investment:
With no related allowance recorded	1,521	2,280	1,532	2,647
With an allowance recorded	2,915	3,971	3,090	4,435
Average recorded investment	4,436	6,251	4,622	7,082
Interest income recognized:
With no related allowance recorded	16	29	47	125
With an allowance recorded	44	74	165	241
Interest income recognized	60	103	212	366
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	6,624		6,624		5,671
With an allowance recorded	22,061		22,061		15,448
Recorded investment	28,685		28,685		21,119
Unpaid principal balance:
With no related allowance recorded	7,637		7,637		6,333
With an allowance recorded	22,434		22,434		16,073
Unpaid principal balance	30,071		30,071		22,406
Related Allowance	4,734		4,734		3,527
Average recorded investment:
With no related allowance recorded	14,352	4,250	9,240	5,659
With an allowance recorded	11,433	18,487	15,075	10,942
Average recorded investment	25,785	22,737	24,315	16,601
Interest income recognized:
With no related allowance recorded	141	3	154	144
With an allowance recorded	65	106	275	192
Interest income recognized	206	109	429	336
Consumer loans
Recorded investment:
With no related allowance recorded	0		0		0
With an allowance recorded	11		11		13
Recorded investment	11		11		13
Unpaid principal balance:
With no related allowance recorded	0		0		0
With an allowance recorded	11		11		13
Unpaid principal balance	11		11		13
Related Allowance	2		2		$ 7
Average recorded investment:
With no related allowance recorded	10	0	3	0
With an allowance recorded	11	14	12	15
Average recorded investment	21	14	15	15
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