Fair Value - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Assets
Securities available-for-sale	$ 235,774,000	$ 404,825,000
Securities held-to-maturity	304,927,000	368,107,000
Federal Home Loan Bank, Federal Reserve Bank stock and other investments, at cost	33,522,000	29,842,000
I/O strips receivables	305,000	503,000
Liabilities
Subordinated Debt.	39,740,000	39,554,000
Significant Other Observable Inputs (Level 2)
Assets
I/O strips receivables	305,000	503,000
Carrying amount
Assets
Cash and cash equivalents	1,131,073,000	457,370,000
Securities available-for-sale	235,774,000	404,825,000
Securities held-to-maturity	297,389,000	366,560,000
Loans (including loans held-for-sale), net	2,576,560,000	2,511,611,000
Federal Home Loan Bank, Federal Reserve Bank stock and other investments, at cost	33,522,000	29,842,000
Accrued interest receivable	10,546,000	10,915,000
I/O strips receivables	305,000	503,000
Liabilities
Time deposits	153,407,000	168,034,000
Other deposits	3,761,079,000	3,246,734,000
Subordinated Debt.	39,740,000	39,554,000
Accrued interest payable	545,000	707,000
Carried at fair value
Assets
Cash and cash equivalents	1,131,073,000	457,370,000
Securities available-for-sale	235,774,000	404,825,000
Securities held-to-maturity	304,927,000	368,107,000
Loans (including loans held-for-sale), net	2,574,692,000	2,513,329,000
Accrued interest receivable	10,546,000	10,915,000
I/O strips receivables	305,000	503,000
Liabilities
Time deposits	153,740,000	158,704,000
Other deposits	3,761,079,000	3,246,734,000
Subordinated Debt.	40,340,000	40,404,000
Accrued interest payable	545,000	707,000
Carried at fair value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash and cash equivalents	1,131,073,000	457,370,000
Securities available-for-sale	60,448,000	120,464,000
Accrued interest receivable	309,000	446,000
Carried at fair value | Significant Other Observable Inputs (Level 2)
Assets
Securities available-for-sale	175,326,000	284,361,000
Securities held-to-maturity	304,927,000	368,107,000
Loans (including loans held-for-sale), net	1,699,000	1,052,000
Accrued interest receivable	1,512,000	2,218,000
I/O strips receivables	305,000	503,000
Liabilities
Time deposits	153,740,000	158,704,000
Other deposits	3,761,079,000	3,246,734,000
Subordinated Debt.	40,340,000	40,404,000
Accrued interest payable	545,000	707,000
Carried at fair value | Significant Unobservable Inputs (Level 3)
Assets
Loans (including loans held-for-sale), net	2,572,993,000	2,512,277,000
Accrued interest receivable	$ 8,725,000	$ 8,251,000