Fair value (Estimated fair value and carrying value) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets, Fair Value Disclosure [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	$ 485,203	$ 510,439
Restricted Cash, at Fair Value	3,030	3,030
Trading Securities	191	347
Available-for-sale Securities	645,797	751,484
Held to maturity Fair Value	497,681	592,763
Federal Home Loan Bank (FHLB) stock	13,995	10,793
Other Investments	3	3
Loans Including HFS Fair Value	3,842,907	3,917,340
Derivative Assets	771	1,330
FDIC Indemnification Asset Fair Value Disclosure	0	8,669
Receivables, Fair Value Disclosure	49,969	20,227
Servicing Assets	9,821	9,858	$ 7,455	$ 13,992
Account Receivable and Other assets, Fair Value	41,898	47,120
Liabilities, Fair Value Disclosure [Abstract]
Deposits, Fair Value Disclosure	4,782,197	4,644,629
Securities sold under agreements to repurchase	191,104	651,898
Advances from FHLB	99,509	106,422
Other Borrowings	153	61
Subordinated capital notes	33,080	30,230
Derivative Liabilities Current	1,281	2,437
Accrued expenses and other liabilities	86,791	95,370
Assets,Carrying Value [Abstract]
Cash and Cash Equivalents, at Carrying Value	485,203	510,439
Restricted Cash And Cash Equivalents	3,030	3,030
Trading Securities	191	347
Investment securities AFS , carrying value	645,797	751,484
Investment held for sale, carrying amount	506,064	599,884
Federal Home Loan Bank Stock at carrying value	13,995	10,793
Other Investment, Carrying Value	3	3
Loans, net of allowance for loan and lease losses	4,037,362	4,129,427
Derivative Assets, carrying value	771	1,330
FDIC Indemnification Asset	0	14,411	$ 22,599	$ 97,378
Accrued interest receivable	49,969	20,227
Servicing assets, carrying value	9,821	9,858
Account receivable and oher assets, carrying value	41,898	47,120
Liabilities,Carrying Value Disclosure [Abstract]
Deposits, Total	4,799,482	4,664,487
Securities Sold under Agreements to Repurchase	192,869	653,756
Advances from FHLB	99,643	105,454
Other Borrowings	153	61
Subordinated capital notes	36,083	36,083
Accrued expenses and other liabilities	86,791	95,370
Derivative liabilities, carrying value	1,281	2,437
Fair Value, Inputs, Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	485,203	510,439
Restricted Cash, at Fair Value	3,030	3,030
Available-for-sale Securities	0	0
Derivative Assets	0	0
Servicing Assets	0	0
Liabilities, Fair Value Disclosure [Abstract]
Derivative Liabilities Current	0	0
Assets,Carrying Value [Abstract]
Cash and Cash Equivalents, at Carrying Value	485,203	510,439
Restricted Cash And Cash Equivalents	3,030	3,030
Trading Securities	0	0
Fair Value, Inputs, Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Trading Securities	191	347
Available-for-sale Securities	645,797	751,484
Held to maturity Fair Value	497,681	592,763
Federal Home Loan Bank (FHLB) stock	13,995	10,793
Other Investments	3	3
Derivative Assets	771	1,330
Servicing Assets	0	0
Liabilities, Fair Value Disclosure [Abstract]
Derivative Liabilities Current	1,281	2,437
Assets,Carrying Value [Abstract]
Trading Securities	191	347
Investment securities AFS , carrying value	645,797	751,484
Investment held for sale, carrying amount	506,064	599,884
Federal Home Loan Bank Stock at carrying value	13,995	10,793
Other Investment, Carrying Value	3	3
Derivative Assets, carrying value	771	1,330
Liabilities,Carrying Value Disclosure [Abstract]
Derivative liabilities, carrying value	1,281	2,437
Fair Value, Inputs, Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	0	0
Loans Including HFS Fair Value	3,842,907	3,917,340
Derivative Assets	0	0
FDIC Indemnification Asset Fair Value Disclosure	0	8,669
Receivables, Fair Value Disclosure	49,969	20,227
Servicing Assets	9,821	9,858
Account Receivable and Other assets, Fair Value	41,898	47,120
Liabilities, Fair Value Disclosure [Abstract]
Deposits, Fair Value Disclosure	4,782,197	4,644,629
Securities sold under agreements to repurchase	191,104	651,898
Advances from FHLB	99,509	106,422
Other Borrowings	153	61
Subordinated capital notes	33,080	30,230
Derivative Liabilities Current	0	0
Accrued expenses and other liabilities	86,791	95,370
Assets,Carrying Value [Abstract]
Trading Securities	0	0
Loans, net of allowance for loan and lease losses	4,056,329	4,147,692
FDIC Indemnification Asset	0	14,411
Accrued interest receivable	49,969	20,227
Servicing assets, carrying value	9,821	9,858
Account receivable and oher assets, carrying value	41,898	47,120
Liabilities,Carrying Value Disclosure [Abstract]
Deposits, Total	4,799,482	4,664,487
Securities Sold under Agreements to Repurchase	192,869	653,756
Advances from FHLB	99,643	105,454
Other Borrowings	153	61
Subordinated capital notes	36,083	36,083
Accrued expenses and other liabilities	$ 86,791	$ 95,370