Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs (Detail) - TDRs By Class - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of TDRs by Class [Line Items]
Total		$ 5,067	$ 23,608	$ 27,853
Commercial And Industrial
Schedule of TDRs by Class [Line Items]
Accruing		294	269
Non-accrual	[1]	1,050	18,799
Total		1,344	19,068
Agricultural
Schedule of TDRs by Class [Line Items]
Accruing		0	0
Non-accrual	[1]	0	0
Total		0	0
Office, Retail, and Industrial
Schedule of TDRs by Class [Line Items]
Accruing		164	586
Non-accrual	[1]	0	0
Total		164	586
Multi-family
Schedule of TDRs by Class [Line Items]
Accruing		598	887
Non-accrual	[1]	186	232
Total		784	1,119
Construction
Schedule of TDRs by Class [Line Items]
Accruing		0	0
Non-accrual	[1]	0	0
Total		0	0
Other Commercial Real Estate
Schedule of TDRs by Class [Line Items]
Accruing		340	433
Non-accrual	[1]	0	183
Total		340	616
Total Commercial Real Estate
Schedule of TDRs by Class [Line Items]
Accruing		1,102	1,906
Non-accrual	[1]	186	415
Total		1,288	2,321
Total Corporate Loans
Schedule of TDRs by Class [Line Items]
Accruing		1,396	2,175
Non-accrual	[1]	1,236	19,214
Total		2,632	21,389
Home equity
Schedule of TDRs by Class [Line Items]
Accruing		494	651
Non-accrual	[1]	667	506
Total		1,161	1,157
1-4 family mortgages
Schedule of TDRs by Class [Line Items]
Accruing		853	878
Non-accrual	[1]	421	184
Total		1,274	1,062
Installment
Schedule of TDRs by Class [Line Items]
Accruing		0	0
Non-accrual	[1]	0	0
Total		0	0
Total consumer loans
Schedule of TDRs by Class [Line Items]
Accruing		1,347	1,529
Non-accrual	[1]	1,088	690
Total		2,435	2,219
Total Loans
Schedule of TDRs by Class [Line Items]
Accruing		2,743	3,704
Non-accrual	[1]	2,324	19,904
Total		$ 5,067	$ 23,608

[1] These TDRs are included in non-accrual loans in the preceding tables.