Loans - Summary of Loan Balances (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Mortgage loans on real estate:
Total mortgage loan on real estate	$ 1,913,024		$ 1,811,832
Consumer:
Total consumer loans	381,114		395,283
Commercial	209,840		194,913
Construction:
Total construction	149,652		120,909
Total loans, net of deferred loan fees and discounts	2,653,630		2,522,937	$ 2,393,762
Total principal balance of loans owed, net of charge-offs	2,683,201		2,555,610
Unamortized net deferred loan fees	(6,259)		(6,551)
Discounts to principal balance of loans owed, net of charge-offs	(23,312)		(26,122)
Total loans, net of unamortized deferred loan fees and discounts	2,653,630		2,522,937	2,393,762
Noncovered loans	2,649,386		2,517,702
Covered loans	4,244		5,235
Total loans, net of unamortized deferred loan fees and discounts	2,653,630		2,522,937	2,393,762
Allowance for loan losses	(35,509)	$ (36,388)	(36,011)	(35,455)	$ (36,055)	$ (36,585)
Residential 1-4 family [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	318,206		314,265
Home Equity Loans [Member]
Consumer:
Total consumer loans	42,002		40,362
Construction:
Total loans, net of deferred loan fees and discounts	42,002		40,362	34,572
Total loans, net of unamortized deferred loan fees and discounts	42,002		40,362	34,572
Total loans, net of unamortized deferred loan fees and discounts	42,002		40,362	34,572
Allowance for loan losses	(3,021)	(3,111)	(3,138)	(2,128)	(1,980)	(1,797)
Other [Member]
Consumer:
Total consumer loans	32,434		32,429
Commercial [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	1,594,818		1,497,567
Construction:
Total construction	87,321		74,774
Home Equity Lines of Credit [Member]
Consumer:
Total consumer loans	306,678		322,492
Construction:
Total loans, net of deferred loan fees and discounts	306,678		322,492	344,115
Total loans, net of unamortized deferred loan fees and discounts	306,678		322,492	344,115
Total loans, net of unamortized deferred loan fees and discounts	306,678		322,492	344,115
Allowance for loan losses	(9,202)	$ (9,907)	(11,253)	$ (13,993)	$ (15,233)	$ (15,676)
Residential [Member]
Construction:
Total construction	62,331		46,135
Originated [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	1,519,318		1,371,228
Consumer:
Total consumer loans	339,989		349,134
Commercial	189,494		170,320
Construction:
Total construction	126,808		98,063
Total loans, net of deferred loan fees and discounts	2,175,609		1,988,745
Total principal balance of loans owed, net of charge-offs	2,181,868		1,995,296
Unamortized net deferred loan fees	(6,259)		(6,551)
Total loans, net of unamortized deferred loan fees and discounts	2,175,609		1,988,745
Noncovered loans	2,175,609		1,988,745
Total loans, net of unamortized deferred loan fees and discounts	2,175,609		1,988,745
Allowance for loan losses	(30,362)		(31,271)
Originated [Member] | Residential 1-4 family [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	221,460		207,585
Originated [Member] | Home Equity Loans [Member]
Consumer:
Total consumer loans	36,517		34,717
Originated [Member] | Other [Member]
Consumer:
Total consumer loans	29,623		28,998
Originated [Member] | Commercial [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	1,297,858		1,163,643
Construction:
Total construction	78,200		66,285
Originated [Member] | Home Equity Lines of Credit [Member]
Consumer:
Total consumer loans	273,849		285,419
Originated [Member] | Residential [Member]
Construction:
Total construction	48,608		31,778
PNCI [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	376,139		415,399
Consumer:
Total consumer loans	33,181		36,720
Commercial	16,062		19,744
Construction:
Total construction	22,295		22,125
Total loans, net of deferred loan fees and discounts	447,677		493,988
Total principal balance of loans owed, net of charge-offs	459,359		507,935
Discounts to principal balance of loans owed, net of charge-offs	(11,682)		(13,947)
Total loans, net of unamortized deferred loan fees and discounts	447,677		493,988
Noncovered loans	447,677		493,988
Total loans, net of unamortized deferred loan fees and discounts	447,677		493,988
Allowance for loan losses	(2,339)		(1,848)
PNCI [Member] | Residential 1-4 family [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	95,121		104,535
PNCI [Member] | Home Equity Loans [Member]
Consumer:
Total consumer loans	3,854		4,018
PNCI [Member] | Other [Member]
Consumer:
Total consumer loans	2,748		3,367
PNCI [Member] | Commercial [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	281,018		310,864
Construction:
Total construction	9,121		8,489
PNCI [Member] | Home Equity Lines of Credit [Member]
Consumer:
Total consumer loans	26,579		29,335
PNCI [Member] | Residential [Member]
Construction:
Total construction	13,174		13,636
PCI - Cash basis [Member]
Consumer:
Total consumer loans	4,216		5,078
Commercial			1
Construction:
Total loans, net of deferred loan fees and discounts	4,216		5,079
Total principal balance of loans owed, net of charge-offs	11,025		12,686
Discounts to principal balance of loans owed, net of charge-offs	(6,809)		(7,607)
Total loans, net of unamortized deferred loan fees and discounts	4,216		5,079
Noncovered loans	4,216		5,079
Total loans, net of unamortized deferred loan fees and discounts	4,216		5,079
Allowance for loan losses	(16)		(121)
PCI - Cash basis [Member] | Home Equity Loans [Member]
Consumer:
Total consumer loans	124		124
PCI - Cash basis [Member] | Home Equity Lines of Credit [Member]
Consumer:
Total consumer loans	4,092		4,954
PCI - Other [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	17,567		25,205
Consumer:
Total consumer loans	3,728		4,351
Commercial	4,284		4,848
Construction:
Total construction	549		721
Total loans, net of deferred loan fees and discounts	26,128		35,125
Total principal balance of loans owed, net of charge-offs	30,949		39,693
Discounts to principal balance of loans owed, net of charge-offs	(4,821)		(4,568)
Total loans, net of unamortized deferred loan fees and discounts	26,128		35,125
Noncovered loans	21,884		29,890
Covered loans	4,244		5,235
Total loans, net of unamortized deferred loan fees and discounts	26,128		35,125
Allowance for loan losses	(2,792)		(2,771)
PCI - Other [Member] | Residential 1-4 family [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	1,625		2,145
PCI - Other [Member] | Home Equity Loans [Member]
Consumer:
Total consumer loans	1,507		1,503
PCI - Other [Member] | Other [Member]
Consumer:
Total consumer loans	63		64
PCI - Other [Member] | Commercial [Member]
Mortgage loans on real estate:
Total mortgage loan on real estate	15,942		23,060
PCI - Other [Member] | Home Equity Lines of Credit [Member]
Consumer:
Total consumer loans	2,158		2,784
PCI - Other [Member] | Residential [Member]
Construction:
Total construction	$ 549		$ 721