Allowance for Credit Losses - Schedule of Allowance for Loan Losses and Carrying Amount of Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Allowance for Loan Losses:
Beginning balance				$ 73,901				$ 73,874	$ 73,901	$ 73,874
Charge-offs									21,006	20,555
Recoveries									2,036	2,720
Provision	4,343	4,777	4,960	5,187	5,947	4,346	3,436	4,133	19,267	17,862	17,141
Ending balance	74,198				73,901				74,198	73,901	73,874
Ending Balance: individually evaluated for impairment	12,477				13,790				12,477	13,790
Ending Balance: collectively evaluated for impairment	61,721				60,111				61,721	60,111
Ending Balance: loans acquired with deteriorated credit quality	0				0				0	0
Financing receivables:
Ending balance	6,713,599				6,517,780				6,713,599	6,517,780
Ending Balance: individually evaluated for impairment	81,302				81,940				81,302	81,940
Ending Balance: collectively evaluated for impairment	6,601,198				6,402,634				6,601,198	6,402,634
Ending Balance: loans acquired with deteriorated credit quality	31,099				33,206				31,099	33,206
Owner-Occupied [Member]
Allowance for Loan Losses:
Beginning balance				3,877				3,670	3,877	3,670
Charge-offs									5,344	801
Recoveries									150	60
Provision									6,970	948
Ending balance	5,653				3,877				5,653	3,877
Ending Balance: individually evaluated for impairment	638				417				638	417
Ending Balance: collectively evaluated for impairment	5,015				3,460				5,015	3,460
Ending Balance: loans acquired with deteriorated credit quality	0				0				0	0
Financing receivables:
Ending balance	654,963				728,906				654,963	728,906
Ending Balance: individually evaluated for impairment	7,157				14,474				7,157	14,474
Ending Balance: collectively evaluated for impairment	646,548				712,776				646,548	712,776
Ending Balance: loans acquired with deteriorated credit quality	1,258				1,656				1,258	1,656
Nonowner-Occupied [Member]
Allowance for Loan Losses:
Beginning balance				12,876				11,647	12,876	11,647
Charge-offs									1,164	2,608
Recoveries									56	122
Provision									(2,776)	3,715
Ending balance	8,992				12,876				8,992	12,876
Ending Balance: individually evaluated for impairment	1,631				1,154				1,631	1,154
Ending Balance: collectively evaluated for impairment	7,361				11,722				7,361	11,722
Ending Balance: loans acquired with deteriorated credit quality	0				0				0	0
Financing receivables:
Ending balance	1,917,785				1,740,420				1,917,785	1,740,420
Ending Balance: individually evaluated for impairment	13,913				12,101				13,913	12,101
Ending Balance: collectively evaluated for impairment	1,894,421				1,718,913				1,894,421	1,718,913
Ending Balance: loans acquired with deteriorated credit quality	9,451				9,406				9,451	9,406
Other Commercial [Member]
Allowance for Loan Losses:
Beginning balance				20,511				20,803	20,511	20,803
Charge-offs									7,699	3,619
Recoveries									641	1,362
Provision									7,464	1,965
Ending balance	20,917				20,511				20,917	20,511
Ending Balance: individually evaluated for impairment	2,192				7,564				2,192	7,564
Ending Balance: collectively evaluated for impairment	18,725				12,947				18,725	12,947
Ending Balance: loans acquired with deteriorated credit quality	0				0				0	0
Financing receivables:
Ending balance	1,338,355				1,377,083				1,338,355	1,377,083
Ending Balance: individually evaluated for impairment	22,327				28,997				22,327	28,997
Ending Balance: collectively evaluated for impairment	1,314,543				1,346,600				1,314,543	1,346,600
Ending Balance: loans acquired with deteriorated credit quality	1,485				1,486				1,485	1,486
Residential Real Estate [Member]
Allowance for Loan Losses:
Beginning balance				14,895				13,880	14,895	13,880
Charge-offs									4,111	8,882
Recoveries									698	821
Provision									5,212	9,076
Ending balance	16,694				14,895				16,694	14,895
Ending Balance: individually evaluated for impairment	4,112				996				4,112	996
Ending Balance: collectively evaluated for impairment	12,582				13,899				12,582	13,899
Ending Balance: loans acquired with deteriorated credit quality	0				0				0	0
Financing receivables:
Ending balance	1,821,378				1,838,252				1,821,378	1,838,252
Ending Balance: individually evaluated for impairment	16,160				8,541				16,160	8,541
Ending Balance: collectively evaluated for impairment	1,802,686				1,826,196				1,802,686	1,826,196
Ending Balance: loans acquired with deteriorated credit quality	2,532				3,515				2,532	3,515
Construction & Land Development [Member]
Allowance for Loan Losses:
Beginning balance				18,858				19,151	18,858	19,151
Charge-offs									896	3,099
Recoveries									73	54
Provision									918	2,752
Ending balance	18,953				18,858				18,953	18,858
Ending Balance: individually evaluated for impairment	3,752				3,659				3,752	3,659
Ending Balance: collectively evaluated for impairment	15,201				15,199				15,201	15,199
Ending Balance: loans acquired with deteriorated credit quality	0				0				0	0
Financing receivables:
Ending balance	670,364				550,677				670,364	550,677
Ending Balance: individually evaluated for impairment	21,593				17,827				21,593	17,827
Ending Balance: collectively evaluated for impairment	632,407				515,718				632,407	515,718
Ending Balance: loans acquired with deteriorated credit quality	16,364				17,132				16,364	17,132
Consumer [Member]
Allowance for Loan Losses:
Beginning balance				2,620				2,151	2,620	2,151
Charge-offs									1,792	1,546
Recoveries									418	301
Provision									1,699	1,714
Ending balance	2,945				2,620				2,945	2,620
Ending Balance: individually evaluated for impairment	152				0				152	0
Ending Balance: collectively evaluated for impairment	2,793				2,620				2,793	2,620
Ending Balance: loans acquired with deteriorated credit quality	0				0				0	0
Financing receivables:
Ending balance	310,754				282,442				310,754	282,442
Ending Balance: individually evaluated for impairment	152				0				152	0
Ending Balance: collectively evaluated for impairment	310,593				282,431				310,593	282,431
Ending Balance: loans acquired with deteriorated credit quality	9				11				9	11
Allowance for Estimated Imprecision [Member]
Allowance for Loan Losses:
Beginning balance				264				2,572	264	2,572
Charge-offs									0	0
Recoveries									0	0
Provision									(220)	(2,308)
Ending balance	44				264				44	264
Ending Balance: individually evaluated for impairment	0				0				0	0
Ending Balance: collectively evaluated for impairment	44				264				44	264
Ending Balance: loans acquired with deteriorated credit quality	0				0				0	0
Financing receivables:
Ending balance	0				0				0	0
Ending Balance: individually evaluated for impairment	0				0				0	0
Ending Balance: collectively evaluated for impairment	0				0				0	0
Ending Balance: loans acquired with deteriorated credit quality	$ 0				$ 0				$ 0	$ 0