Loans - Summary of Troubled Debt Restructurings, Excluding Purchased Non-Covered and Covered Loans, by Collateral Types (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 21,200	$ 20,900	$ 23,300
Excluding Purchased Non-Covered and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	18,848	17,214	18,513
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	80	72	52
Troubled debt restructuring loans	18,848	17,214	18,513
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Warehouse [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4	4	3
Troubled debt restructuring loans	1,345	1,346	1,689
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Raw Land [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	5	11	1
Troubled debt restructuring loans	1,298	2,345	1,285
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Troubled debt restructuring loans	311
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Hotel & Motel [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	3	3
Troubled debt restructuring loans	2,154	2,185	2,273
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Office [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4	4	4
Troubled debt restructuring loans	1,652	1,909	2,095
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Retail, Including Strip Centers [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	6	4	6
Troubled debt restructuring loans	2,905	1,095	2,821
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | 1-4 Family Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	42	36	30
Troubled debt restructuring loans	8,027	7,747	7,550
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Church [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Troubled debt restructuring loans	365
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Automobile/Equipment/Inventory [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	13	8	3
Troubled debt restructuring loans	548	92	500
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Unsecured [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1	1
Troubled debt restructuring loans	243	245	50
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Life Insurance Policy [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts		1	1
Troubled debt restructuring loans		250	250
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	18	20	8
Troubled debt restructuring loans	2,365	3,683	4,755
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Warehouse [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	2	1
Troubled debt restructuring loans	586	592	176
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Raw Land [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	2	1
Troubled debt restructuring loans	29	32	43
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Troubled debt restructuring loans	66
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Office [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1		1
Troubled debt restructuring loans	149		2,450
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Retail, Including Strip Centers [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	2	1
Troubled debt restructuring loans	516	1,680	969
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | 1-4 Family Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	9	9	3
Troubled debt restructuring loans	978	852	1,111
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Automobile/Equipment/Inventory [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	4	1
Troubled debt restructuring loans	41	479	6
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Unsecured [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts		1
Troubled debt restructuring loans		$ 48