Fair Value - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Assets
Securities available-for-sale	$ 459,043,000	$ 391,852,000
Securities held-to-maturity	366,175,000	394,292,000
Federal Home Loan Bank and Federal Reserve Bank stock and other investments, at cost	25,216,000	17,911,000
I/O strips receivables	568,000	968,000
Liabilities
Subordinated Debt.	39,369,000	39,183,000
Significant Other Observable Inputs (Level 2)
Assets
I/O strips receivables	568,000	968,000
Carrying amount
Assets
Cash and cash equivalents	164,568,000	316,222,000
Securities available-for-sale	459,043,000	391,852,000
Securities held-to-maturity	377,198,000	398,341,000
Loans (including loans held-for-sale), net	1,861,206,000	1,566,428,000
Federal Home Loan Bank and Federal Reserve Bank stock and other investments, at cost	25,216,000	17,911,000
Accrued interest receivable	9,577,000	7,985,000
I/O strips receivables	568,000	968,000
Liabilities
Time deposits	147,560,000	194,561,000
Other deposits	2,489,972,000	2,288,428,000
Subordinated Debt.	39,369,000	39,183,000
Accrued interest payable	497,000	389,000
Carried at fair value
Assets
Cash and cash equivalents	164,568,000	316,222,000
Securities available-for-sale	459,043,000	391,852,000
Securities held-to-maturity	366,175,000	394,292,000
Loans (including loans held-for-sale), net	1,829,303,000	1,511,386,000
Accrued interest receivable	9,577,000	7,985,000
I/O strips receivables	568,000	968,000
Liabilities
Time deposits	147,916,000	194,844,000
Other deposits	2,489,972,000	2,288,428,000
Subordinated Debt.	38,969,000	40,384,000
Accrued interest payable	497,000	389,000
Carried at fair value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash and cash equivalents	164,568,000	316,222,000
Carried at fair value | Significant Other Observable Inputs (Level 2)
Assets
Securities available-for-sale	459,043,000	391,852,000
Securities held-to-maturity	366,175,000	394,292,000
Loans (including loans held-for-sale), net	2,649,000	3,419,000
Accrued interest receivable	2,871,000	2,423,000
I/O strips receivables	568,000	968,000
Liabilities
Time deposits	147,916,000	194,844,000
Other deposits	2,489,972,000	2,288,428,000
Subordinated Debt.	38,969,000	40,384,000
Accrued interest payable	497,000	389,000
Carried at fair value | Significant Unobservable Inputs (Level 3)
Assets
Loans (including loans held-for-sale), net	1,826,654,000	1,507,967,000
Accrued interest receivable	$ 6,706,000	$ 5,562,000