Income Taxes - Components of Net Deferred Tax Asset (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Federal [Member]
Deferred tax assets:
Bad debt and credit loss deduction	$ 23,805	$ 29,700
Net operating loss carryforward	672	781
Deferred compensation	3,300	3,024
Other intangibles	5	8
PCI loans	23,667	26,360
California franchise tax	3,461	1,629
Unrealized loss on investment securities, net	0	5,012
Other, net	6,140	4,907
Gross deferred tax asset	61,050	71,421
Deferred tax liabilities:
Depreciation	4,019	5,489
Intangibles - acquistions	1,858	2,024
FDIC indemnification asset	13,831	14,269
FHLB stock	3,913	4,388
Deferred income	2,430	2,706
Unrealized gain on investment securities, net	16,695	0
Gross deferred tax liability	42,746	28,876
Net deferred tax asset	18,304	42,545
State [Member]
Deferred tax assets:
Bad debt and credit loss deduction	6,014	8,226
Net operating loss carryforward	34	34
Deferred compensation	1,030	942
Other intangibles	668	620
FDIC indemnification asset	6,498	6,363
Unrealized loss on investment securities, net	0	1,744
Other, net	1,911	1,554
Gross deferred tax asset	16,155	19,483
Deferred tax liabilities:
Depreciation	(589)	(1,058)
PCI loans	4,389	3,935
FHLB stock	(797)	(945)
Deferred income	(374)	(479)
Unrealized gain on investment securities, net	(5,808)	0
Gross deferred tax liability	11,957	6,417
Net deferred tax asset	$ 4,198	$ 13,066