Fair Value - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Assets
Securities available-for-sale	$ 145,955,000	$ 235,774,000
Securities held-to-maturity	426,755,000	304,927,000
Federal Home Loan Bank, Federal Reserve Bank stock and other investments, at cost	32,495,000	33,522,000
I/O strips receivables	274,000	305,000
Liabilities
Subordinated Debt.	39,832,000	39,740,000
Significant Other Observable Inputs (Level 2)
Assets
I/O strips receivables	274,000	305,000
Carrying amount
Assets
Cash and cash equivalents	1,328,322,000	1,131,073,000
Securities available-for-sale	145,955,000	235,774,000
Securities held-to-maturity	421,286,000	297,389,000
Loans (including loans held-for-sale), net	2,785,184,000	2,576,560,000
Federal Home Loan Bank, Federal Reserve Bank stock and other investments, at cost	32,495,000	33,522,000
Accrued interest receivable	10,397,000	10,546,000
I/O strips receivables	274,000	305,000
Liabilities
Time deposits	158,644,000	153,407,000
Other deposits	4,185,828,000	3,761,079,000
Subordinated Debt.	39,832,000	39,740,000
Accrued interest payable	548,000	545,000
Carried at fair value
Assets
Cash and cash equivalents	1,328,322,000	1,131,073,000
Securities available-for-sale	145,955,000	235,774,000
Securities held-to-maturity	426,755,000	304,927,000
Loans (including loans held-for-sale), net	2,800,683,000	2,574,692,000
Accrued interest receivable	10,397,000	10,546,000
I/O strips receivables	274,000	305,000
Liabilities
Time deposits	158,843,000	153,740,000
Other deposits	4,185,828,000	3,761,079,000
Subordinated Debt.	40,432,000	40,340,000
Accrued interest payable	548,000	545,000
Carried at fair value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash and cash equivalents	1,328,322,000	1,131,073,000
Securities available-for-sale	15,063,000	60,448,000
Accrued interest receivable	103,000	309,000
Carried at fair value | Significant Other Observable Inputs (Level 2)
Assets
Securities available-for-sale	130,892,000	175,326,000
Securities held-to-maturity	426,755,000	304,927,000
Loans (including loans held-for-sale), net	4,344,000	1,699,000
Accrued interest receivable	1,510,000	1,512,000
I/O strips receivables	274,000	305,000
Liabilities
Time deposits	158,843,000	153,740,000
Other deposits	4,185,828,000	3,761,079,000
Subordinated Debt.	40,432,000	40,340,000
Accrued interest payable	548,000	545,000
Carried at fair value | Significant Unobservable Inputs (Level 3)
Assets
Loans (including loans held-for-sale), net	2,796,339,000	2,572,993,000
Accrued interest receivable	$ 8,784,000	$ 8,725,000