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, Excluding PCI Loans by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				$ 75,235					$ 75,235
Provision for loan losses	0	(1,000)	(7,600)	(7,500)	(6,800)	(3,750)	(6,200)	0	(16,100)	(16,750)	0
Ending Balance	59,825				75,235				59,825	75,235
Loans, Excluding PCI Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				75,235				92,441	75,235	92,441	93,964
Charge-offs									(2,369)	(2,851)	(5,207)
Recoveries									3,059	2,395	3,027
Provision for loan losses									(16,100)	(16,750)	657
Ending Balance	59,825				75,235				59,825	75,235	92,441
Loans, Excluding PCI Loans [Member] | Commercial and industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				8,502				8,901	8,502	8,901	8,030
Charge-offs									(888)	(2,491)	(1,158)
Recoveries									873	544	876
Provision for loan losses									(1,413)	1,548	1,153
Ending Balance	7,074				8,502				7,074	8,502	8,901
Loans, Excluding PCI Loans [Member] | Small Business Administration [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				2,332				2,751	2,332	2,751	2,624
Charge-offs									(50)	0	(101)
Recoveries									114	215	404
Provision for loan losses									161	(634)	(176)
Ending Balance	2,557				2,332				2,557	2,332	2,751
Loans, Excluding PCI Loans [Member] | Commercial real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				39,402				47,457	39,402	47,457	47,841
Charge-offs									(353)	0	(1,873)
Recoveries									140	402	514
Provision for loan losses									(5,816)	(8,457)	975
Ending Balance	33,373				39,402				33,373	39,402	47,457
Loans, Excluding PCI Loans [Member] | Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				1,305				2,291	1,305	2,291	4,947
Charge-offs									0	0	0
Recoveries									885	703	1,139
Provision for loan losses									(1,202)	(1,689)	(3,795)
Ending Balance	988				1,305				988	1,305	2,291
Loans, Excluding PCI Loans [Member] | SFR mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				2,718				3,448	2,718	3,448	4,032
Charge-offs									0	(252)	(642)
Recoveries									401	367	(108)
Provision for loan losses									(775)	(845)	166
Ending Balance	2,344				2,718				2,344	2,718	3,448
Loans, Excluding PCI Loans [Member] | Dairy & livestock and agribusiness [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				11,728				18,696	11,728	18,696	17,278
Charge-offs									(1,061)	0	(1,150)
Recoveries									492	109	166
Provision for loan losses									(5,680)	(7,077)	2,402
Ending Balance	5,479				11,728				5,479	11,728	18,696
Loans, Excluding PCI Loans [Member] | Municipal lease finance receivables [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				2,335				1,588	2,335	1,588	2,403
Charge-offs									0	0	0
Recoveries									0	0	0
Provision for loan losses									(923)	747	(815)
Ending Balance	1,412				2,335				1,412	2,335	1,588
Loans, Excluding PCI Loans [Member] | Consumer and other loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				960				1,170	960	1,170	1,590
Charge-offs									(17)	(108)	(283)
Recoveries									154	55	36
Provision for loan losses									165	(157)	(173)
Ending Balance	1,262				960				1,262	960	1,170
Loans, Excluding PCI Loans [Member] | Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				5,953				6,139	5,953	6,139	5,219
Charge-offs									0	0	0
Recoveries									0	0	0
Provision for loan losses									(617)	(186)	920
Ending Balance	$ 5,336				$ 5,953				$ 5,336	$ 5,953	$ 6,139