Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs (Detail) - Impaired Loans Individually Evaluated by Class (Continued) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Average Recorded Balance		$ 26,366	$ 48,163	$ 65,916
Interest income recognized	[1]	390	759	262
Commercial And Industrial
Financing Receivable, Impaired [Line Items]
Average Recorded Balance		8,940	16,137	20,925
Interest income recognized	[1]	163	371	205
Agricultural
Financing Receivable, Impaired [Line Items]
Average Recorded Balance		0	0	0
Interest income recognized	[1]	0	0	0
Office, Retail, and Industrial
Financing Receivable, Impaired [Line Items]
Average Recorded Balance		9,359	19,003	24,802
Interest income recognized	[1]	52	245	18
Multi-family
Financing Receivable, Impaired [Line Items]
Average Recorded Balance		855	1,245	1,116
Interest income recognized	[1]	13	5	8
Construction
Financing Receivable, Impaired [Line Items]
Average Recorded Balance		3,902	5,764	5,932
Interest income recognized	[1]	118	0	0
Other Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Average Recorded Balance		3,310	6,014	13,141
Interest income recognized	[1]	44	138	31
Total Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Average Recorded Balance		17,426	32,026	44,991
Interest income recognized	[1]	$ 227	$ 388	$ 57

[1] Recorded using the cash basis of accounting.