Accounting for Certain Loans Acquired in a Transfer - Amounts of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		$ 3,636,841
Allowance for Loan Losses	$ 48,440	17,667
Carrying Amount	$ 3,658,859
Loans Purchased With Evidence of Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		14,630
Allowance for Loan Losses		133
Carrying Amount		14,497
Loans Purchased With Evidence of Credit Deterioration | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		10,205
Loans Purchased With Evidence of Credit Deterioration | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		3,443
Loans Purchased With Evidence of Credit Deterioration | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		982
Loans Purchased With Evidence of Credit Deterioration | Heartland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		296
Allowance for Loan Losses		0
Carrying Amount		296
Loans Purchased With Evidence of Credit Deterioration | Heartland | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		197
Loans Purchased With Evidence of Credit Deterioration | Heartland | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		99
Loans Purchased With Evidence of Credit Deterioration | Heartland | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		0
Loans Purchased With Evidence of Credit Deterioration | Summit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		561
Allowance for Loan Losses		0
Carrying Amount		561
Loans Purchased With Evidence of Credit Deterioration | Summit | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		88
Loans Purchased With Evidence of Credit Deterioration | Summit | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		473
Loans Purchased With Evidence of Credit Deterioration | Summit | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		0
Loans Purchased With Evidence of Credit Deterioration | Peoples
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		264
Allowance for Loan Losses		0
Carrying Amount		264
Loans Purchased With Evidence of Credit Deterioration | Peoples | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		229
Loans Purchased With Evidence of Credit Deterioration | Peoples | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		35
Loans Purchased With Evidence of Credit Deterioration | Peoples | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		0
Loans Purchased With Evidence of Credit Deterioration | Kosciusko
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		375
Allowance for Loan Losses		0
Carrying Amount		375
Loans Purchased With Evidence of Credit Deterioration | Kosciusko | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		244
Loans Purchased With Evidence of Credit Deterioration | Kosciusko | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		131
Loans Purchased With Evidence of Credit Deterioration | Kosciusko | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		0
Loans Purchased With Evidence of Credit Deterioration | LaPorte
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		1,166
Allowance for Loan Losses		0
Carrying Amount		1,166
Loans Purchased With Evidence of Credit Deterioration | LaPorte | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		353
Loans Purchased With Evidence of Credit Deterioration | LaPorte | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		793
Loans Purchased With Evidence of Credit Deterioration | LaPorte | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		20
Loans Purchased With Evidence of Credit Deterioration | Lafayette
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		1,867
Allowance for Loan Losses		0
Carrying Amount		1,867
Loans Purchased With Evidence of Credit Deterioration | Lafayette | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		1,867
Loans Purchased With Evidence of Credit Deterioration | Lafayette | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		0
Loans Purchased With Evidence of Credit Deterioration | Lafayette | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		0
Loans Purchased With Evidence of Credit Deterioration | Wolverine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		2,289
Allowance for Loan Losses		0
Carrying Amount		2,289
Loans Purchased With Evidence of Credit Deterioration | Wolverine | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		2,289
Loans Purchased With Evidence of Credit Deterioration | Wolverine | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		0
Loans Purchased With Evidence of Credit Deterioration | Wolverine | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		0
Loans Purchased With Evidence of Credit Deterioration | Salin
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		7,812
Allowance for Loan Losses		133
Carrying Amount		7,679
Loans Purchased With Evidence of Credit Deterioration | Salin | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		4,938
Loans Purchased With Evidence of Credit Deterioration | Salin | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		1,912
Loans Purchased With Evidence of Credit Deterioration | Salin | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding Balance		$ 962