Loan and Lease Finance Receivables and Allowance for Credit Losses - Schedule of Held-for-Investment and Held-for-Sale Loans, Individually Evaluated for Impairment by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	$ 112,721	$ 108,390
Unpaid Principal Balance	130,423	125,631
Related Allowance	4,071	2,332
Average Recorded Investment	111,542	110,479
Interest Income Recognized	674	2,300
With no related allowance recorded [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	103,025	99,925
Unpaid Principal Balance	119,467	116,800
Average Recorded Investment	101,742	102,609
Interest Income Recognized	674	2,227
With no related allowance recorded [Member] | Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	2,873	3,385
Unpaid Principal Balance	3,617	4,215
Average Recorded Investment	2,899	3,766
Interest Income Recognized	18	43
With no related allowance recorded [Member] | Construction - speculative [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	18,272	21,314
Unpaid Principal Balance	18,607	21,607
Average Recorded Investment	18,272	21,650
Interest Income Recognized	77	311
With no related allowance recorded [Member] | Construction - non-speculative [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	9,219	9,219
Unpaid Principal Balance	9,219	9,219
Average Recorded Investment	9,219	9,219
Interest Income Recognized	141	574
With no related allowance recorded [Member] | Commercial real estate - owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	13,616	13,478
Unpaid Principal Balance	14,827	14,569
Average Recorded Investment	13,630	14,459
Interest Income Recognized	122	397
With no related allowance recorded [Member] | Commercial real estate - non-owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	27,877	28,639
Unpaid Principal Balance	38,306	38,633
Average Recorded Investment	28,092	29,801
Interest Income Recognized	202	670
With no related allowance recorded [Member] | Residential real estate (SFR 1-4) [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	10,184	11,079
Unpaid Principal Balance	12,821	14,342
Average Recorded Investment	10,319	11,292
Interest Income Recognized	16	54
With no related allowance recorded [Member] | Dairy and livestock [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	20,843	12,406
Unpaid Principal Balance	21,874	13,756
Average Recorded Investment	19,170	11,834
Interest Income Recognized	98	173
With no related allowance recorded [Member] | Municipal Lease Finance Receivables [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment		263
Unpaid Principal Balance		263
Related Allowance
Average Recorded Investment		443
Interest Income Recognized		5
With no related allowance recorded [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	141	142
Unpaid Principal Balance	196	196
Average Recorded Investment	141	145
With no related allowance recorded [Member] | Auto and equipment leases [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment
Unpaid Principal Balance
Related Allowance
Average Recorded Investment
Interest Income Recognized
With a Related Allowance Recorded [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	9,696	8,465
Unpaid Principal Balance	10,956	8,831
Related Allowance	4,071	2,332
Average Recorded Investment	9,800	7,870
Interest Income Recognized		73
With a Related Allowance Recorded [Member] | Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	1,706	304
Unpaid Principal Balance	1,871	327
Related Allowance	1,055	289
Average Recorded Investment	1,723	387
With a Related Allowance Recorded [Member] | Construction - speculative [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment
Unpaid Principal Balance
Related Allowance
Average Recorded Investment
Interest Income Recognized
With a Related Allowance Recorded [Member] | Construction - non-speculative [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment
Unpaid Principal Balance
Related Allowance
Average Recorded Investment
Interest Income Recognized
With a Related Allowance Recorded [Member] | Commercial real estate - owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	12	19
Unpaid Principal Balance	14	19
Related Allowance	1	2
Average Recorded Investment	16	28
With a Related Allowance Recorded [Member] | Commercial real estate - non-owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment
Unpaid Principal Balance
Related Allowance
Average Recorded Investment
Interest Income Recognized
With a Related Allowance Recorded [Member] | Residential real estate (SFR 1-4) [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	3,409	3,766
Unpaid Principal Balance	4,040	4,071
Related Allowance	428	434
Average Recorded Investment	3,415	3,363
With a Related Allowance Recorded [Member] | Dairy and livestock [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	4,484	4,303
Unpaid Principal Balance	4,944	4,340
Related Allowance	2,560	1,596
Average Recorded Investment	4,603	4,017
Interest Income Recognized		73
With a Related Allowance Recorded [Member] | Municipal Lease Finance Receivables [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment
Unpaid Principal Balance
Related Allowance
Average Recorded Investment
Interest Income Recognized
With a Related Allowance Recorded [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	20	73
Unpaid Principal Balance	22	74
Related Allowance	7	11
Average Recorded Investment	21	75
With a Related Allowance Recorded [Member] | Auto and equipment leases [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	65
Unpaid Principal Balance	65
Related Allowance	20
Average Recorded Investment	22
Interest Income Recognized