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, 2017	Sep. 30, 2016	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	$ 16,899	$ 26,993	$ 26,018
Recorded Investment, With a related allowance recorded	409	8,691	367
Recorded Investment, Total impaired loans	17,308	35,684	26,385
Unpaid Principal Balance, With no related allowance recorded	20,616	33,938	32,198
Unpaid Principal Balance, With a related allowance recorded	434	8,768	383
Unpaid Principal Balance, Total impaired loans	21,050	42,706	32,581
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	88	548	141
Related Allowance, Total impaired loans	88	548	141
Average Recorded Investment, With no related allowance recorded	17,766	28,014
Average Recorded Investment, With a related allowance recorded	439	8,816
Average Recorded Investment, Total impaired loans	18,205	36,830
Interest Income Recognized, With no related allowance recorded	277	379
Interest Income Recognized, With a related allowance recorded	1	313
Interest Income Recognized, Total impaired loans	278	692
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	726	786	730
Recorded Investment, With a related allowance recorded	19	563	171
Unpaid Principal Balance, With no related allowance recorded	1,256	1,687	1,646
Unpaid Principal Balance, With a related allowance recorded	20	625	171
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	2	493	114
Average Recorded Investment, With no related allowance recorded	870	858
Average Recorded Investment, With a related allowance recorded	42	671
Interest Income Recognized, With no related allowance recorded	15	20
Interest Income Recognized, With a related allowance recorded	1	8
Small Business Administration [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	2,270	3,665	3,386
Recorded Investment, With a related allowance recorded	3	202	196
Unpaid Principal Balance, With no related allowance recorded	2,573	4,452	4,189
Unpaid Principal Balance, With a related allowance recorded	20	217	212
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	3	33	27
Average Recorded Investment, With no related allowance recorded	2,489	3,770
Average Recorded Investment, With a related allowance recorded	7	209
Interest Income Recognized, With no related allowance recorded	38	38
Interest Income Recognized, With a related allowance recorded	0	10
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	4,313	2,773	1,797
Recorded Investment, With a related allowance recorded	0	0	0
Unpaid Principal Balance, With no related allowance recorded	4,625	3,786	2,276
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	4,361	3,039
Average Recorded Investment, With a related allowance recorded	0	0
Interest Income Recognized, With no related allowance recorded	42	63
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	3,855	13,033	13,331
Recorded Investment, With a related allowance recorded	0	0	0
Unpaid Principal Balance, With no related allowance recorded	5,155	15,764	15,842
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	4,010	13,386
Average Recorded Investment, With a related allowance recorded	0	0
Interest Income Recognized, With no related allowance recorded	72	130
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	0	7,651	0
Unpaid Principal Balance, With no related allowance recorded	0	0	0
Unpaid Principal Balance, With a related allowance recorded	0	7,651	0
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	0	4	0
Average Recorded Investment, With no related allowance recorded	0	0
Average Recorded Investment, With a related allowance recorded	0	7,651
Interest Income Recognized, With no related allowance recorded	0	0
Interest Income Recognized, With a related allowance recorded	0	291
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	4,550	5,239	5,174
Recorded Investment, With a related allowance recorded	0	263	0
Unpaid Principal Balance, With no related allowance recorded	5,345	6,118	6,075
Unpaid Principal Balance, With a related allowance recorded	0	263	0
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	0	6	0
Average Recorded Investment, With no related allowance recorded	4,620	5,370
Average Recorded Investment, With a related allowance recorded	0	273
Interest Income Recognized, With no related allowance recorded	109	93
Interest Income Recognized, With a related allowance recorded	0	4
Dairy & Livestock and Agribusiness [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment, With no related allowance recorded	829	659	747
Recorded Investment, With a related allowance recorded	0	0	0
Unpaid Principal Balance, With no related allowance recorded	1,091	722	747
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	1,035	695
Average Recorded Investment, With a related allowance recorded	0	0
Interest Income Recognized, With no related allowance recorded	1	24
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	356	838	853
Recorded Investment, With a related allowance recorded	387	12	0
Unpaid Principal Balance, With no related allowance recorded	571	1,409	1,423
Unpaid Principal Balance, With a related allowance recorded	394	12	0
Related Allowance, With no related allowance recorded	0	0	0
Related Allowance, With a related allowance recorded	83	12	$ 0
Average Recorded Investment, With no related allowance recorded	381	896
Average Recorded Investment, With a related allowance recorded	390	12
Interest Income Recognized, With no related allowance recorded	0	11
Interest Income Recognized, With a related allowance recorded	$ 0	$ 0