Loans and Other Repossessed Assets Acquired (Detail) - Analysis of changes in allowance for loan losses (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011	Dec. 31, 2011
Allowance for loan losses
Balance at beginning of period	$ 48,799		$ 55,491	$ 53,524		$ 88,349
Provision for loan losses	4,533		8,940	15,975		99,418
Loan charge-offs	(7,615)		(10,759)	(25,343)		(135,941)
Recoveries	634		661	2,195		2,507
Net charge-offs	(6,981)		(10,098)	(23,148)		(133,434)
Balance at end of period	46,351		54,333	46,351		54,333
Loans as of September 30, 2012
Individually evaluated for impairment	24,594		25,673	24,594		25,673
Collectively evaluated for impairment	2,404,195		2,311,760	2,404,195		2,311,760
ASC 310-30 loans	145,580		17,901	145,580		17,901
Total loans	2,574,369		2,355,334	2,574,369		2,355,334	2,385,457
Residential Loans [Member]
Allowance for loan losses
Balance at beginning of period	7,929		7,649	8,748		9,955
Provision for loan losses	1,000		726	2,537		16,291
Loan charge-offs	(730)		(688)	(3,359)		(18,882)
Recoveries	33		109	306		432
Net charge-offs	(697)		(579)	(3,053)		(18,450)
Balance at end of period	8,232		7,796	8,232		7,796
Loans as of September 30, 2012
Individually evaluated for impairment	5,902		1,028	5,902		1,028
Collectively evaluated for impairment	1,055,429		965,603	1,055,429		965,603
ASC 310-30 loans	19,075	[1]	432	19,075	[1]	432
Total loans	1,080,406	[1]	967,063	1,080,406	[1]	967,063	1,032,134
Consumer Loan [Member]
Allowance for loan losses
Balance at beginning of period	21,581		22,836	22,581		22,014
Provision for loan losses	1,352		5,350	8,669		17,883
Loan charge-offs	(2,730)		(6,655)	(11,506)		(18,918)
Recoveries	412		392	871		944
Net charge-offs	(2,318)		(6,263)	(10,635)		(17,974)
Balance at end of period	20,615		21,923	20,615		21,923
Loans as of September 30, 2012
Individually evaluated for impairment	6,432		2,393	6,432		2,393
Collectively evaluated for impairment	755,007		750,684	755,007		750,684
ASC 310-30 loans	10,937	[1]	544	10,937	[1]	544
Total loans	772,376	[1]	753,621	772,376	[1]	753,621	735,253
Commercial Business [Member]
Allowance for loan losses
Balance at beginning of period	3,988		4,339	4,106		8,558
Provision for loan losses	410		282	1,450		4,717
Loan charge-offs	(1,045)		(194)	(2,357)		(8,979)
Recoveries	121		58	275		189
Net charge-offs	(924)		(136)	(2,082)		(8,790)
Balance at end of period	3,474		4,485	3,474		4,485
Loans as of September 30, 2012
Individually evaluated for impairment	761		3,147	761		3,147
Collectively evaluated for impairment	91,775		75,973	91,775		75,973
ASC 310-30 loans	32,809		1,751	32,809		1,751
Total loans	125,345		80,871	125,345		80,871
Commercial Real Estate [Member]
Allowance for loan losses
Balance at beginning of period	10,272		12,044	11,711		25,159
Provision for loan losses	1,909		380	2,646		30,481
Loan charge-offs	(2,042)		(459)	(4,808)		(43,829)
Recoveries	48		26	638		180
Net charge-offs	(1,994)		(433)	(4,170)		(43,649)
Balance at end of period	10,187		11,991	10,187		11,991
Loans as of September 30, 2012
Individually evaluated for impairment	9,025		13,583	9,025		13,583
Collectively evaluated for impairment	456,660		448,223	456,660		448,223
ASC 310-30 loans	54,450		9,490	54,450		9,490
Total loans	520,135		471,296	520,135		471,296
Commercial Construction [Member]
Allowance for loan losses
Balance at beginning of period	231		1,064	397		1,723
Provision for loan losses	(182)		236	(350)		2,641
Loan charge-offs	(14)		(645)	(14)		(3,743)
Recoveries	3		10	5		44
Net charge-offs	(11)		(635)	(9)		(3,699)
Balance at end of period	38		665	38		665
Loans as of September 30, 2012
Individually evaluated for impairment	248		261	248		261
Collectively evaluated for impairment	1,881		14,225	1,881		14,225
ASC 310-30 loans	(328)		565	(328)		565
Total loans	1,801		15,051	1,801		15,051
Commercial Land [Member]
Allowance for loan losses
Balance at beginning of period	4,798		7,559	5,981		20,940
Provision for loan losses	44		1,966	1,023		27,405
Loan charge-offs	(1,054)		(2,118)	(3,299)		(41,590)
Recoveries	17		66	100		718
Net charge-offs	(1,037)		(2,052)	(3,199)		(40,872)
Balance at end of period	3,805		7,473	3,805		7,473
Loans as of September 30, 2012
Individually evaluated for impairment	2,226		5,261	2,226		5,261
Collectively evaluated for impairment	43,443		57,052	43,443		57,052
ASC 310-30 loans	28,637		5,119	28,637		5,119
Total loans	$ 74,306		$ 67,432	$ 74,306		$ 67,432

[1] Credit quality indicators are reviewed and updated as applicable on an ongoing basis in accordance with credit policies.