Bank segment - Credit risk profile - payment activity (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Credit risk profile based on payment activity for loans
Total past due	$ 19,716	$ 23,102
Current	4,710,076	4,720,517
Total financing receivables	4,729,792	4,743,619
Recorded Investment greater than 90 days and accruing	0	0
Residential 1-4 family
Credit risk profile based on payment activity for loans
Total past due	9,958	11,310
Current	2,048,244	2,036,741
Total financing receivables	2,058,202	2,048,051
Recorded Investment greater than 90 days and accruing	0	0
Commercial real estate
Credit risk profile based on payment activity for loans
Total past due	0	2,416
Current	790,191	797,979
Total financing receivables	790,191	800,395
Recorded Investment greater than 90 days and accruing	0	0
Home equity line of credit
Credit risk profile based on payment activity for loans
Total past due	2,697	2,986
Current	864,183	860,177
Total financing receivables	866,880	863,163
Recorded Investment greater than 90 days and accruing	0	0
Residential land
Credit risk profile based on payment activity for loans
Total past due	397	255
Current	16,491	18,634
Total financing receivables	16,888	18,889
Recorded Investment greater than 90 days and accruing	0	0
Commercial construction
Credit risk profile based on payment activity for loans
Total past due	0	0
Current	130,808	126,768
Total financing receivables	130,808	126,768
Recorded Investment greater than 90 days and accruing	0	0
Residential construction
Credit risk profile based on payment activity for loans
Total past due	0	0
Current	13,694	16,080
Total financing receivables	13,694	16,080
Recorded Investment greater than 90 days and accruing	0	0
Commercial loans
Credit risk profile based on payment activity for loans
Total past due	3,030	2,226
Current	657,986	689,825
Total financing receivables	661,016	692,051
Recorded Investment greater than 90 days and accruing	0	0
Consumer loans
Credit risk profile based on payment activity for loans
Total past due	3,634	3,909
Current	188,479	174,313
Total financing receivables	192,113	178,222
Recorded Investment greater than 90 days and accruing	0	0
30-59 days past due
Credit risk profile based on payment activity for loans
Total past due	7,215	11,504
30-59 days past due | Residential 1-4 family
Credit risk profile based on payment activity for loans
Total past due	3,557	5,467
30-59 days past due | Commercial real estate
Credit risk profile based on payment activity for loans
Total past due	0	2,416
30-59 days past due | Home equity line of credit
Credit risk profile based on payment activity for loans
Total past due	594	1,263
30-59 days past due | Residential land
Credit risk profile based on payment activity for loans
Total past due	0	0
30-59 days past due | Commercial construction
Credit risk profile based on payment activity for loans
Total past due	0	0
30-59 days past due | Residential construction
Credit risk profile based on payment activity for loans
Total past due	0	0
30-59 days past due | Commercial loans
Credit risk profile based on payment activity for loans
Total past due	1,255	413
30-59 days past due | Consumer loans
Credit risk profile based on payment activity for loans
Total past due	1,809	1,945
60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	5,716	4,230
60-89 days past due | Residential 1-4 family
Credit risk profile based on payment activity for loans
Total past due	2,982	2,338
60-89 days past due | Commercial real estate
Credit risk profile based on payment activity for loans
Total past due	0	0
60-89 days past due | Home equity line of credit
Credit risk profile based on payment activity for loans
Total past due	571	381
60-89 days past due | Residential land
Credit risk profile based on payment activity for loans
Total past due	318	0
60-89 days past due | Commercial construction
Credit risk profile based on payment activity for loans
Total past due	0	0
60-89 days past due | Residential construction
Credit risk profile based on payment activity for loans
Total past due	0	0
60-89 days past due | Commercial loans
Credit risk profile based on payment activity for loans
Total past due	928	510
60-89 days past due | Consumer loans
Credit risk profile based on payment activity for loans
Total past due	917	1,001
Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	6,785	7,368
Greater than 90 days | Residential 1-4 family
Credit risk profile based on payment activity for loans
Total past due	3,419	3,505
Greater than 90 days | Commercial real estate
Credit risk profile based on payment activity for loans
Total past due	0	0
Greater than 90 days | Home equity line of credit
Credit risk profile based on payment activity for loans
Total past due	1,532	1,342
Greater than 90 days | Residential land
Credit risk profile based on payment activity for loans
Total past due	79	255
Greater than 90 days | Commercial construction
Credit risk profile based on payment activity for loans
Total past due	0	0
Greater than 90 days | Residential construction
Credit risk profile based on payment activity for loans
Total past due	0	0
Greater than 90 days | Commercial loans
Credit risk profile based on payment activity for loans
Total past due	847	1,303
Greater than 90 days | Consumer loans
Credit risk profile based on payment activity for loans
Total past due	$ 908	$ 963