Loans and Other Repossessed Assets Acquired (Detail) - Loan portfolio by major category (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Loans receivable gross	$ 2,476,142	$ 2,495,324	$ 2,355,567
Less: Allowance for loan losses	47,427	44,179	50,776	53,524
Net loans	2,428,715	2,451,145	2,304,791
Residential Loans [Member] \| Residential 1-4 Family [Member]
Loans receivable gross	963,053	956,355
Residential Loans [Member] \| Residential Construction [Member]
Loans receivable gross	25,895	22,439
Residential Loans [Member] \| Residential Land [Member]
Loans receivable gross	48,911	52,739
Residential Loans [Member]
Loans receivable gross	1,037,859	1,031,533	1,029,176
Less: Allowance for loan losses	8,388	7,790	7,581	8,748
Commercial Loan [Member] \| Commercial Business [Member]
Loans receivable gross	130,169	118,379
Commercial Loan [Member] \| Commercial Real Estate [Member]
Loans receivable gross	467,890	491,567
Commercial Loan [Member] \| Commercial Construction [Member]
Loans receivable gross	1,092	1,064
Commercial Loan [Member] \| Commercial Land [Member]
Loans receivable gross	64,582	70,109
Commercial Loan [Member]
Loans receivable gross	663,733	681,119
Consumer Loan [Member] \| Home Equity Loans [Member]
Loans receivable gross	373,108	384,664
Consumer Loan [Member] \| Manufactured Housing [Member]
Loans receivable gross	282,114	280,100
Consumer Loan [Member] \| Marine [Member]
Loans receivable gross	79,328	75,736
Consumer Loan [Member] \| Other Consumer [Member]
Loans receivable gross	40,000	42,172
Consumer Loan [Member]
Loans receivable gross	774,550	782,672	719,923
Less: Allowance for loan losses	19,942	20,403	22,390	22,581
Commercial Business [Member]
Loans receivable gross	130,169		88,054
Less: Allowance for loan losses	4,630	3,066	4,000	4,106
Commercial Real Estate [Member]
Loans receivable gross	467,890		447,339
Less: Allowance for loan losses	11,078	10,099	10,816	11,711
Commercial Construction [Member]
Loans receivable gross	1,092		16,289
Less: Allowance for loan losses	31	16	401	397
Commercial Land [Member]
Loans receivable gross	64,582		54,786
Less: Allowance for loan losses	$ 3,358	$ 2,805	$ 5,588	$ 5,981

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 8, 9

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (b)(1)(ii)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(d))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher OTS

-Name Federal Regulation (FR)

-Number Title 12

-Section 563c.102

-Paragraph 8

-Subparagraph a(ii)

-Chapter V

-Subsection I

-LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Subparagraph d

-Article 9

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 114

-Paragraph 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section L

-Subsection 1

+ Details

- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References+ Details