Fair Value Measurements - Estimated fair value of company's financial instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets
Federal funds sold	$ 28,200	$ 38,987
Interest bearing deposits with other banks	1,752,420	195,447
Estimated Fair Value	1,150,885	843,165
Bank owned life insurance	76,729	75,724
Liabilities
Interest bearing deposits	756,923	863,856
Customer repurchase agreements	26,726	30,980
Fair Value, Inputs, Level 1
Assets
Cash and due from banks	8,435	7,539
Fair Value, Inputs, Level 2
Assets
Cash and due from banks	0	0
Federal funds sold	28,200	38,987
Interest bearing deposits with other banks	1,752,420	195,447
Estimated Fair Value	1,149,385	832,432
Federal Reserve and Federal Home Loan Bank stock	40,104	35,194
Fair Value	88,205	56,707
Bank owned life insurance	76,729	75,724
Annuity investment	14,468	14,697
Liabilities
Noninterest bearing deposits	2,809,334	2,064,367
Interest bearing deposits	756,923	3,876,985
Time deposits	993,500	1,291,688
Customer repurchase agreements	26,726	30,980
Borrowings	575,435	328,330
Fair Value, Inputs, Level 2 | Interest Rate Swap
Liabilities
Derivative liability	516	203
Fair Value, Inputs, Level 2 | Credit Risk Contract
Liabilities
Derivative liability	118	86
Fair Value, Inputs, Level 2 | Interest Rate Caps
Assets
Derivative asset	3,413
Liabilities
Derivative liability	3,574	312
Fair Value, Inputs, Level 2 | Mortgage Banking Derivative
Assets
Derivative asset	0	280
Liabilities
Derivative liability		0
Fair Value, Inputs, Level 3
Assets
Estimated Fair Value	1,500	10,931
Loans	7,608,687	7,550,249
Fair Value, Inputs, Level 3 | Mortgage Banking Derivative
Assets
Derivative asset	5,213
Liabilities
Derivative liability		66
Carrying Value
Assets
Cash and due from banks	8,435	7,539
Federal funds sold	28,200	38,987
Interest bearing deposits with other banks	1,752,420	195,447
Estimated Fair Value	1,150,885	843,363
Federal Reserve and Federal Home Loan Bank stock	40,104	35,194
Fair Value	88,205	56,707
Loans	7,650,633	7,472,090
Bank owned life insurance	76,729	75,724
Annuity investment	14,468	14,697
Liabilities
Noninterest bearing deposits	2,809,334	2,064,367
Interest bearing deposits	756,923	3,876,985
Time deposits	977,760	1,283,039
Customer repurchase agreements	26,726	30,980
Borrowings	568,077	467,687
Carrying Value | Interest Rate Swap
Liabilities
Derivative liability	516	203
Carrying Value | Credit Risk Contract
Liabilities
Derivative liability	118	86
Carrying Value | Interest Rate Caps
Assets
Derivative asset	3,413
Liabilities
Derivative liability	3,574	312
Carrying Value | Mortgage Banking Derivative
Assets
Derivative asset	5,213	280
Liabilities
Derivative liability		66
Fair Value
Assets
Cash and due from banks	8,435	7,539
Federal funds sold	28,200	38,987
Interest bearing deposits with other banks	1,752,420	195,447
Estimated Fair Value	1,150,885	843,363
Federal Reserve and Federal Home Loan Bank stock	40,104	35,194
Fair Value	88,205	56,707
Loans	7,608,687	7,550,249
Bank owned life insurance	76,729	75,724
Annuity investment	14,468	14,697
Liabilities
Noninterest bearing deposits	2,809,334	2,064,367
Interest bearing deposits	756,923	3,876,985
Time deposits	993,500	1,291,688
Customer repurchase agreements	26,726	30,980
Borrowings	575,435	328,330
Fair Value | Interest Rate Swap
Liabilities
Derivative liability	516	203
Fair Value | Credit Risk Contract
Liabilities
Derivative liability	118	86
Fair Value | Interest Rate Caps
Assets
Derivative asset	3,413
Liabilities
Derivative liability	3,574	312
Fair Value | Mortgage Banking Derivative
Assets
Derivative asset	$ 5,213	280
Liabilities
Derivative liability		$ 66