Loans - Amounts of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage warehouse, Total	$ 3,867,383		$ 3,634,596
Total loans			3,636,841
Allowance for loan losses	(57,027)		(17,667)	$ (17,820)	$ (16,394)
Allowance for credit losses	(57,027)	$ (22,577)	(17,667)
Loans, net	3,810,356		3,619,174
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial/Consumer, Total			2,046,651
Mortgage warehouse, Total	2,192,271		2,047,646
Allowance for credit losses	(42,210)		(11,996)
Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage warehouse, Total	1,019,912		920,998
Real Estate, Total			770,717
Allowance for credit losses	(4,620)		(923)
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial/Consumer, Total			669,180
Mortgage warehouse, Total	655,200		665,952
Allowance for credit losses	(8,930)		(3,671)
Working capital and equipment | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial/Consumer, Total			938,317
Real estate, including agriculture | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial/Consumer, Total			978,891
Tax exempt | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial/Consumer, Total			63,571
Other | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial/Consumer, Total			65,872
1-4 family | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real Estate, Total			762,571
Other | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real Estate, Total			8,146
Auto | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial/Consumer, Total			362,729
Recreation | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial/Consumer, Total			16,262
Real estate/home improvement | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial/Consumer, Total			43,585
Home equity | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial/Consumer, Total			237,979
Mortgage warehouse, Total	259,643		276,215
Unsecured | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial/Consumer, Total			7,286
Other | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial/Consumer, Total			1,339
Mortgage warehouse
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage warehouse, Total			150,293
Allowance for credit losses	$ (1,267)	$ 0	$ (1,077)