Loans - Amounts of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage warehouse	$ 119,876	$ 144,692
Total loans	1,720,072	1,749,131
Allowance for loan losses	(14,236)	(14,534)	$ (16,634)	$ (16,501)
Loans, net	1,705,836	1,734,597
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial, Total	797,754	804,995
Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real Estate, Total	442,806	437,144
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer, Total	359,636	362,300
Working Capital and Equipment [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial, Total	381,425	381,245
Real Estate Including Agriculture [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial, Total	381,256	391,668
Tax Exempt Loans Receivable [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial, Total	9,072	8,674
Other Commercial Loans [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial, Total	26,001	23,408
1-4 Family [Member] | Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real Estate, Total	438,391	433,015
Other Real Estate Loans [Member] | Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real Estate, Total	4,415	4,129
Auto [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer, Total	164,600	168,397
Recreation Consumer Loans Receivable [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer, Total	5,021	5,365
Real Estate Home Improvement Loans Receivable [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer, Total	49,114	47,015
Home Equity Loan [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer, Total	125,556	127,113
Unsecured Debt [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer, Total	3,836	4,120
Other Consumer Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer, Total	$ 11,509	$ 10,290