Loans and Lease Finance Receivables and Allowance for Loan Losses - Schedule of Balance and Activity Related to Allowance for Loan Losses for Held-for-Investment Loans by Type (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	$ 60,201	$ 60,938	$ 61,540	$ 59,156
Charge-offs	(147)	(7)	(149)	(195)
Recoveries	2,077	2,070	6,240	4,040
(Recapture of) provision for loan losses	(1,500)	(2,000)	(7,000)	(2,000)
Ending Balance	60,631	61,001	60,631	61,001
PCI Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	659	310	1,219	0
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
(Recapture of) provision for loan losses	(228)	290	(788)	600
Ending Balance	431	600	431	600
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	8,060	9,387	8,154	8,588
Charge-offs	(138)	0	(138)	(85)
Recoveries	12	49	106	253
(Recapture of) provision for loan losses	129	30	(59)	710
Ending Balance	8,063	9,466	8,063	9,466
Small Business Administration [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	913	1,177	871	993
Charge-offs	0	0	0	0
Recoveries	5	6	47	9
(Recapture of) provision for loan losses	(54)	(179)	(54)	2
Ending Balance	864	1,004	864	1,004
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	39,927	39,919	37,443	36,995
Charge-offs	0	0	0	0
Recoveries	0	156	154	791
(Recapture of) provision for loan losses	943	(1,267)	3,273	1,022
Ending Balance	40,870	38,808	40,870	38,808
Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	1,059	1,228	1,096	2,389
Charge-offs	0	0	0	0
Recoveries	2,055	1,731	5,774	2,615
(Recapture of) provision for loan losses	(2,181)	(1,851)	(5,937)	(3,896)
Ending Balance	933	1,108	933	1,108
SFR Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	2,369	2,501	2,287	2,103
Charge-offs	0	0	0	(102)
Recoveries	0	0	64	0
(Recapture of) provision for loan losses	(49)	70	(31)	570
Ending Balance	2,320	2,571	2,320	2,571
Dairy & Livestock and Agribusiness [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	5,440	4,882	8,541	6,029
Charge-offs	0	0	0	0
Recoveries	0	0	19	206
(Recapture of) provision for loan losses	(66)	1,089	(3,186)	(264)
Ending Balance	5,374	5,971	5,374	5,971
Municipal Lease Finance Receivables [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	852	1,115	941	1,153
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
(Recapture of) provision for loan losses	54	(82)	(35)	(120)
Ending Balance	906	1,033	906	1,033
Consumer and Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	922	419	988	906
Charge-offs	(9)	(7)	(11)	(8)
Recoveries	5	128	76	166
(Recapture of) provision for loan losses	(48)	(100)	(183)	(624)
Ending Balance	$ 870	$ 440	$ 870	$ 440