Loans and Allowance for Loan Losses - Major classifications of loans (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Classifications of loans
Total loans	$ 4,193,560	$ 4,175,008	$ 4,127,566
Less allowance for loan losses	(105,753)	(107,137)	(113,601)
Loans, net	4,087,807	4,067,871	4,013,965
Loans Receivable
Classifications of loans
Total loans	4,193,560	4,175,008	4,127,566
Less allowance for loan losses	(105,753)	(107,137)	(113,601)	(114,468)
Loans, net	4,087,807	4,067,871	4,013,965
Loans Receivable \| Commercial (secured by real estate)
Classifications of loans
Total loans	1,804,030	1,813,365	1,843,207
Less allowance for loan losses	(30,408)	(27,847)	(30,614)	(31,644)
Loans Receivable \| Commercial & industrial
Classifications of loans
Total loans	453,764	458,246	439,496
Less allowance for loan losses	(5,626)	(5,537)	(5,472)	(5,681)
Loans Receivable \| Commercial construction
Classifications of loans
Total loans	152,410	154,769	167,122
Less allowance for loan losses	(8,108)	(8,389)	(9,583)	(6,097)
Loans Receivable \| Residential mortgage
Classifications of loans
Total loans	1,245,975	1,214,203	1,131,248
Less allowance for loan losses	(26,928)	(26,642)	(27,356)	(29,076)
Loans Receivable \| Residential construction
Classifications of loans
Total loans	371,733	381,677	435,375
Less allowance for loan losses	(23,326)	(26,662)	(29,473)	(30,379)
Loans Receivable \| Consumer installment
Classifications of loans
Total loans	165,648	152,748	111,118
Less allowance for loan losses	(2,092)	(2,747)	(1,898)	(2,124)
Loans Receivable \| Commercial
Classifications of loans
Total loans	2,410,204	2,426,380	2,449,825
Loans Receivable \| Commercial \| Commercial (secured by real estate)
Classifications of loans
Total loans	1,804,030	1,813,365	1,843,207
Loans Receivable \| Commercial \| Commercial & industrial
Classifications of loans
Total loans	453,764	458,246	439,496
Loans Receivable \| Commercial \| Commercial construction
Classifications of loans
Total loans	$ 152,410	$ 154,769	$ 167,122

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 before allowance and after 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

- 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