Past Due Loans, Allowances For Credit Losses, Impaired Loans, and TDRs (Detail) - TDRs By Class (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Schedule of TDRs by Class [Line Items]
Total	$ 23,608		$ 27,853		$ 17,791
Commercial And Industrial
Schedule of TDRs by Class [Line Items]
Accruing	269		6,538
Non-accrual	18,799	[1]	2,121	[1]
Total	19,068		8,659
Agricultural
Schedule of TDRs by Class [Line Items]
Accruing	0		0
Non-accrual	0	[1]	0	[1]
Total	0		0
Office Retail And Industrial
Schedule of TDRs by Class [Line Items]
Accruing	586		10,271
Non-accrual	0	[1]	0	[1]
Total	586		10,271
Multi-Family
Schedule of TDRs by Class [Line Items]
Accruing	887		1,038
Non-accrual	232	[1]	253	[1]
Total	1,119		1,291
Construction
Schedule of TDRs by Class [Line Items]
Accruing	0		0
Non-accrual	0	[1]	0	[1]
Total	0		0
Other Commercial Real Estate
Schedule of TDRs by Class [Line Items]
Accruing	433		4,326
Non-accrual	183	[1]	291	[1]
Total	616		4,617
Total Commercial Real Estate
Schedule of TDRs by Class [Line Items]
Accruing	1,906		15,635
Non-accrual	415	[1]	544	[1]
Total	2,321		16,179
Total Corporate Loans
Schedule of TDRs by Class [Line Items]
Accruing	2,175		22,173
Non-accrual	19,214	[1]	2,665	[1]
Total	21,389		24,838
Home equity
Schedule of TDRs by Class [Line Items]
Accruing	651		787
Non-accrual	506	[1]	512	[1]
Total	1,157		1,299
1-4 family mortgages
Schedule of TDRs by Class [Line Items]
Accruing	878		810
Non-accrual	184	[1]	906	[1]
Total	1,062		1,716
Installment
Schedule of TDRs by Class [Line Items]
Accruing	0		0
Non-accrual	0	[1]	0	[1]
Total	0		0
Total consumer loans
Schedule of TDRs by Class [Line Items]
Accruing	1,529		1,597
Non-accrual	690	[1]	1,418	[1]
Total	2,219		3,015
Total Loans
Schedule of TDRs by Class [Line Items]
Accruing	3,704		23,770
Non-accrual	19,904	[1]	4,083	[1]
Total	$ 23,608		$ 27,853

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