Loans - Summary of Loan Balances (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
Mortgage loans on real estate:
Total mortgage loan on real estate	$ 1,214,153		$ 1,107,863
Consumer:
Total consumer loans	373,620		383,163
Commercial	135,085		131,878
Construction:
Total construction	43,013		49,103
Total loans, net of deferred loan fees and discounts	1,765,871		1,672,007
Total principal balance of loans owed, net of charge-offs	1,793,323		1,703,380
Unamortized net deferred loan fees	(4,641)		(3,694)
Discounts to principal balance of loans owed, net of charge-offs	(22,811)		(27,679)
Total loans, net of unamortized deferred loan fees and discounts	1,765,871		1,672,007
Noncovered loans	1,741,652		1,644,095
Covered loans	24,219		27,912
Total loans, net of unamortized deferred loan fees and discounts	1,765,871		1,672,007
Allowance for loan losses	(37,920)	(39,968)	(38,245)	(39,340)	(39,599)	(42,648)
Auto Indirect [Member]
Consumer:
Total consumer loans	212		946
Other [Member]
Consumer:
Total consumer loans	29,088		27,763
Residential 1-4 family [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	228,407		195,013
Commercial [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	985,746		912,850
Construction:
Total construction	18,627		17,170
Home equity lines of credit [Member]
Consumer:
Total consumer loans	321,942		339,866
Home equity loans [Member]
Consumer:
Total consumer loans	22,378		14,588
Residential [Member]
Construction:
Total construction	24,386		31,933
Originated [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	1,048,831		954,794
Consumer:
Total consumer loans	350,017		356,610
Commercial	128,791		124,650
Construction:
Total construction	41,413		47,492
Total loans, net of deferred loan fees and discounts	1,569,052		1,483,546
Total principal balance of loans owed, net of charge-offs	1,573,693		1,487,240
Unamortized net deferred loan fees	(4,641)		(3,694)
Discounts to principal balance of loans owed, net of charge-offs	0
Total loans, net of unamortized deferred loan fees and discounts	1,569,052		1,483,546
Noncovered loans	1,569,052		1,483,546
Covered loans	0
Total loans, net of unamortized deferred loan fees and discounts	1,569,052		1,483,546
Allowance for loan losses	(31,249)		(31,354)
Originated [Member] | Auto Indirect [Member]
Consumer:
Total consumer loans	212		946
Originated [Member] | Other [Member]
Consumer:
Total consumer loans	27,201		25,608
Originated [Member] | Residential 1-4 family [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	141,854		129,882
Originated [Member] | Commercial [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	906,977		824,912
Construction:
Total construction	18,553		17,125
Originated [Member] | Home equity lines of credit [Member]
Consumer:
Total consumer loans	300,995		316,207
Originated [Member] | Home equity loans [Member]
Consumer:
Total consumer loans	21,609		13,849
Originated [Member] | Residential [Member]
Construction:
Total construction	22,860		30,367
PNCI [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	134,836		118,153
Consumer:
Total consumer loans	13,720		15,903
Commercial	474		693
Construction:
Total construction	0
Total loans, net of deferred loan fees and discounts	149,030		134,749
Total principal balance of loans owed, net of charge-offs	154,730		142,786
Unamortized net deferred loan fees	0
Discounts to principal balance of loans owed, net of charge-offs	(5,700)		(8,037)
Total loans, net of unamortized deferred loan fees and discounts	149,030		134,749
Noncovered loans	149,030		134,749
Covered loans	0
Total loans, net of unamortized deferred loan fees and discounts	149,030		134,749
Allowance for loan losses	(3,262)		(2,850)
PNCI [Member] | Auto Indirect [Member]
Consumer:
Total consumer loans	0
PNCI [Member] | Other [Member]
Consumer:
Total consumer loans	1,823		2,074
PNCI [Member] | Residential 1-4 family [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	82,766		60,475
PNCI [Member] | Commercial [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	52,070		57,678
Construction:
Total construction	0
PNCI [Member] | Home equity lines of credit [Member]
Consumer:
Total consumer loans	11,744		13,576
PNCI [Member] | Home equity loans [Member]
Consumer:
Total consumer loans	153		253
PNCI [Member] | Residential [Member]
Construction:
Total construction	0
PCI - Cash basis [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	0
Consumer:
Total consumer loans	5,671		6,200
Commercial	9		19
Construction:
Total construction	0
Total loans, net of deferred loan fees and discounts	5,680		6,219
Total principal balance of loans owed, net of charge-offs	14,981		16,475
Unamortized net deferred loan fees	0
Discounts to principal balance of loans owed, net of charge-offs	(9,301)		(10,256)
Total loans, net of unamortized deferred loan fees and discounts	5,680		6,219
Noncovered loans	5,680		6,219
Covered loans	0
Total loans, net of unamortized deferred loan fees and discounts	5,680		6,219
Allowance for loan losses	(398)		(385)
PCI - Cash basis [Member] | Auto Indirect [Member]
Consumer:
Total consumer loans	0
PCI - Cash basis [Member] | Other [Member]
Consumer:
Total consumer loans	0
PCI - Cash basis [Member] | Residential 1-4 family [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	0
PCI - Cash basis [Member] | Commercial [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	0
Construction:
Total construction	0
PCI - Cash basis [Member] | Home equity lines of credit [Member]
Consumer:
Total consumer loans	5,545		6,200
PCI - Cash basis [Member] | Home equity loans [Member]
Consumer:
Total consumer loans	126
PCI - Cash basis [Member] | Residential [Member]
Construction:
Total construction	0
PCI - Other [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	30,486		34,916
Consumer:
Total consumer loans	4,212		4,450
Commercial	5,811		6,516
Construction:
Total construction	1,600		1,611
Total loans, net of deferred loan fees and discounts	42,109		47,493
Total principal balance of loans owed, net of charge-offs	49,919		56,879
Unamortized net deferred loan fees	0
Discounts to principal balance of loans owed, net of charge-offs	(7,810)		(9,386)
Total loans, net of unamortized deferred loan fees and discounts	42,109		47,493
Noncovered loans	17,890		19,581
Covered loans	24,219		27,912
Total loans, net of unamortized deferred loan fees and discounts	42,109		47,493
Allowance for loan losses	(3,011)		(3,656)
PCI - Other [Member] | Auto Indirect [Member]
Consumer:
Total consumer loans	0
PCI - Other [Member] | Other [Member]
Consumer:
Total consumer loans	64		81
PCI - Other [Member] | Residential 1-4 family [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	3,787		4,656
PCI - Other [Member] | Commercial [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	26,699		30,260
Construction:
Total construction	74		45
PCI - Other [Member] | Home equity lines of credit [Member]
Consumer:
Total consumer loans	3,658		3,883
PCI - Other [Member] | Home equity loans [Member]
Consumer:
Total consumer loans	490		486
PCI - Other [Member] | Residential [Member]
Construction:
Total construction	$ 1,526		$ 1,566