Loans and Lease Finance Receivables and Allowance for Loan Losses - Schedule of Held-for-Investment Loans, Excluding PCI Loans, Individually Evaluated for Impairment by Class of Loans (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	$ 26,993	$ 59,889	$ 54,757
Recorded Investment, With a related allowance recorded	8,691	8,972	8,949
Recorded Investment, Total impaired loans	35,684	68,861	63,706
Unpaid Principal Balance, With no related allowance recorded	33,938	69,002	61,984
Unpaid Principal Balance, With a related allowance recorded	8,768	9,104	9,078
Unpaid Principal Balance, Total impaired loans	42,706	78,106	71,062
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	548	662	669
Related Allowance, Total impaired loans	548	662	669
Average Recorded Investment, With no related allowance recorded	28,014	61,818
Average Recorded Investment, With a related allowance recorded	8,816	9,014
Average Recorded Investment, Total impaired loans	36,830	70,832
Interest Income Recognized, With no related allowance recorded	379	1,852
Interest Income Recognized, With a related allowance recorded	313	299
Interest Income Recognized, Total impaired loans	692	2,151
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	786	1,067	1,017
Recorded Investment, With a related allowance recorded	563	620	626
Unpaid Principal Balance, With no related allowance recorded	1,687	1,926	1,894
Unpaid Principal Balance, With a related allowance recorded	625	694	695
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	493	607	626
Average Recorded Investment, With no related allowance recorded	858	1,166
Average Recorded Investment, With a related allowance recorded	671	637
Interest Income Recognized, With no related allowance recorded	20	23
Interest Income Recognized, With a related allowance recorded	8	0
Small Business Administration [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	3,665	3,273	3,207
Recorded Investment, With a related allowance recorded	202	46	41
Unpaid Principal Balance, With no related allowance recorded	4,452	3,911	3,877
Unpaid Principal Balance, With a related allowance recorded	217	47	47
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	33	4	10
Average Recorded Investment, With no related allowance recorded	3,770	3,385
Average Recorded Investment, With a related allowance recorded	209	58
Interest Income Recognized, With no related allowance recorded	38	39
Interest Income Recognized, With a related allowance recorded	10	0
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	2,773	7,665	6,252
Recorded Investment, With a related allowance recorded	0	0	0
Unpaid Principal Balance, With no related allowance recorded	3,786	8,806	7,445
Unpaid Principal Balance, With a related allowance recorded	0	0	0
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	0	0	0
Average Recorded Investment, With no related allowance recorded	3,039	7,935
Average Recorded Investment, With a related allowance recorded	0	0
Interest Income Recognized, With no related allowance recorded	63	178
Interest Income Recognized, With a related allowance recorded	0	0
Commercial Real Estate Non-owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	13,033	35,982	34,041
Recorded Investment, With a related allowance recorded	0	0	0
Unpaid Principal Balance, With no related allowance recorded	15,764	40,591	37,177
Unpaid Principal Balance, With a related allowance recorded	0	0	0
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	0	0	0
Average Recorded Investment, With no related allowance recorded	13,386	36,490
Average Recorded Investment, With a related allowance recorded	0	0
Interest Income Recognized, With no related allowance recorded	130	1,338
Interest Income Recognized, With a related allowance recorded	0	0
Construction Speculative [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	0	0	0
Recorded Investment, With a related allowance recorded	7,651	7,651	7,651
Unpaid Principal Balance, With no related allowance recorded	0	0	0
Unpaid Principal Balance, With a related allowance recorded	7,651	7,651	7,651
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	4	23	13
Average Recorded Investment, With no related allowance recorded	0	0
Average Recorded Investment, With a related allowance recorded	7,651	7,651
Interest Income Recognized, With no related allowance recorded	0	0
Interest Income Recognized, With a related allowance recorded	291	290
Construction Non-speculative [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	0	0	0
Recorded Investment, With a related allowance recorded	0	0	0
Unpaid Principal Balance, With no related allowance recorded	0	0	0
Unpaid Principal Balance, With a related allowance recorded	0	0	0
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	0	0	0
Average Recorded Investment, With no related allowance recorded	0	0
Average Recorded Investment, With a related allowance recorded	0	0
Interest Income Recognized, With no related allowance recorded	0	0
Interest Income Recognized, With a related allowance recorded	0	0
SFR Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	5,239	5,788	5,665
Recorded Investment, With a related allowance recorded	263	601	588
Unpaid Principal Balance, With no related allowance recorded	6,118	6,739	6,453
Unpaid Principal Balance, With a related allowance recorded	263	653	640
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	6	22	20
Average Recorded Investment, With no related allowance recorded	5,370	6,392
Average Recorded Investment, With a related allowance recorded	273	612
Interest Income Recognized, With no related allowance recorded	93	82
Interest Income Recognized, With a related allowance recorded	4	9
Dairy & Livestock and Agribusiness [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	659	5,262	3,685
Recorded Investment, With a related allowance recorded	0	0	0
Unpaid Principal Balance, With no related allowance recorded	722	5,650	3,684
Unpaid Principal Balance, With a related allowance recorded	0	0	0
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	0	0	0
Average Recorded Investment, With no related allowance recorded	695	5,569
Average Recorded Investment, With a related allowance recorded	0	0
Interest Income Recognized, With no related allowance recorded	24	180
Interest Income Recognized, With a related allowance recorded	0	0
Municipal Lease Finance Receivables [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	0	0	0
Recorded Investment, With a related allowance recorded	0	0	0
Unpaid Principal Balance, With no related allowance recorded	0	0	0
Unpaid Principal Balance, With a related allowance recorded	0	0	0
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	0	0	0
Average Recorded Investment, With no related allowance recorded	0	0
Average Recorded Investment, With a related allowance recorded	0	0
Interest Income Recognized, With no related allowance recorded	0	0
Interest Income Recognized, With a related allowance recorded	0	0
Consumer and Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	838	852	890
Recorded Investment, With a related allowance recorded	12	54	43
Unpaid Principal Balance, With no related allowance recorded	1,409	1,379	1,454
Unpaid Principal Balance, With a related allowance recorded	12	59	45
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	12	6	$ 0
Average Recorded Investment, With no related allowance recorded	896	881
Average Recorded Investment, With a related allowance recorded	12	56
Interest Income Recognized, With no related allowance recorded	11	12
Interest Income Recognized, With a related allowance recorded	$ 0	$ 0