Fair Value - Carrying Amount and Estimated Fair Value of Financial Instruments (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Assets
Securities available for sale	$ 652,132,000	$ 1,030,668,000
Securities held to maturity	0	118,955,000
Loans held for sale	43,162,000	11,103,000
Servicing rights, net	3,922,000	4,836,000
Carrying Amount
Assets
Cash and cash equivalents	234,991,000	280,212,000
Securities available for sale	652,132,000	1,030,668,000
Certificates of deposit held at other financial institutions	3,590,000	3,594,000
Securities held to maturity		121,617,000
Loans held for sale	43,162,000	11,103,000
Net loans	2,767,008,000	2,648,948,000
Servicing rights, net	3,246,000	3,403,000
Other assets	225,000	206,000
Accrued interest receivable	12,362,000	13,337,000
Liabilities
Deposits	3,207,584,000	3,431,807,000
Federal Home Loan Bank advances	155,000,000	368,500,000
Subordinated notes	58,872,000	58,693,000
Other liabilities	73,000	129,000
Accrued interest payable	4,201,000	4,700,000
Fair Value
Assets
Cash and cash equivalents	234,991,000	280,212,000
Securities available for sale	652,132,000	1,030,668,000
Certificates of deposit held at other financial institutions	3,590,000	3,594,000
Securities held to maturity		118,955,000
Loans held for sale	43,162,000	11,103,000
Net loans	2,753,761,000	2,622,386,000
Servicing rights, net	3,922,000	4,836,000
Other assets	225,000	206,000
Accrued interest receivable	12,362,000	13,337,000
Liabilities
Deposits	3,208,211,000	3,425,277,000
Federal Home Loan Bank advances	155,090,000	366,786,000
Subordinated notes	60,922,000	59,852,000
Other liabilities	73,000	129,000
Accrued interest payable	4,201,000	4,700,000
Level 1 | Fair Value
Assets
Cash and cash equivalents	234,991,000	280,212,000
Securities available for sale	0	253,014,000
Certificates of deposit held at other financial institutions	0	0
Securities held to maturity		0
Loans held for sale	0	0
Net loans	0	0
Servicing rights, net	0	0
Other assets	0	0
Accrued interest receivable	96,000	71,000
Liabilities
Deposits	2,458,555,000	2,105,951,000
Federal Home Loan Bank advances	0	0
Subordinated notes	0	0
Other liabilities	0	0
Accrued interest payable	154,000	146,000
Level 2 | Fair Value
Assets
Cash and cash equivalents	0	0
Securities available for sale	652,132,000	777,654,000
Certificates of deposit held at other financial institutions	3,590,000	3,594,000
Securities held to maturity		118,955,000
Loans held for sale	43,162,000	11,103,000
Net loans	0	0
Servicing rights, net	0	0
Other assets	225,000	206,000
Accrued interest receivable	3,775,000	5,539,000
Liabilities
Deposits	749,656,000	1,319,326,000
Federal Home Loan Bank advances	155,090,000	366,786,000
Subordinated notes	0	0
Other liabilities	73,000	129,000
Accrued interest payable	687,000	3,866,000
Level 3 | Fair Value
Assets
Cash and cash equivalents	0	0
Securities available for sale	0	0
Certificates of deposit held at other financial institutions	0	0
Securities held to maturity		0
Loans held for sale	0	0
Net loans	2,753,761,000	2,622,386,000
Servicing rights, net	3,922,000	4,836,000
Other assets	0	0
Accrued interest receivable	8,491,000	7,727,000
Liabilities
Deposits	0	0
Federal Home Loan Bank advances	0	0
Subordinated notes	60,922,000	59,852,000
Other liabilities	0	0
Accrued interest payable	$ 3,360,000	$ 688,000