Loans and Allowance for Loan Losses, Financing Receivables Past Due (Details) (USD $)	Mar. 31, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 To 89 days past due and accruing	$ 8,531,000		$ 10,877,000
90 days or more past due and accruing	152,000		0
Total past due and accruing	8,683,000		10,877,000
Nonaccrual	21,836,000	[1]	22,823,000	[1]
Current and accruing	3,741,845,000		3,678,462,000
Total Loans	3,772,364,000		3,712,162,000
Currently performing impaired loans	6,000,000		9,400,000
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 To 89 days past due and accruing	1,681,000		462,000
90 days or more past due and accruing	94,000		0
Total past due and accruing	1,775,000		462,000
Nonaccrual	7,150,000	[1]	8,091,000	[1]
Current and accruing	609,333,000		585,848,000
Total Loans	618,258,000		594,401,000
Unallocated [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 To 89 days past due and accruing	0		41,000
90 days or more past due and accruing	0		0
Total past due and accruing	0		41,000
Nonaccrual	3,915,000	[1]	1,200,000	[1]
Current and accruing	656,466,000		582,554,000
Total Loans	660,381,000		583,795,000
Consumer Real Estate - Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 To 89 days past due and accruing	1,663,000		3,870,000
90 days or more past due and accruing	0		0
Total past due and accruing	1,663,000		3,870,000
Nonaccrual	7,494,000	[1]	5,906,000	[1]
Current and accruing	666,475,000		670,150,000
Total Loans	675,632,000		679,926,000
Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 To 89 days past due and accruing	486,000		3,511,000
90 days or more past due and accruing	0		0
Total past due and accruing	486,000		3,511,000
Nonaccrual	1,799,000	[1]	4,509,000	[1]
Current and accruing	304,148,000		305,532,000
Total Loans	306,433,000		313,552,000
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 To 89 days past due and accruing	4,314,000		2,549,000
90 days or more past due and accruing	0		0
Total past due and accruing	4,314,000		2,549,000
Nonaccrual	1,375,000	[1]	3,038,000	[1]
Current and accruing	1,397,739,000		1,440,991,000
Total Loans	1,403,428,000		1,446,578,000
Consumer and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 To 89 days past due and accruing	387,000		444,000
90 days or more past due and accruing	58,000		0
Total past due and accruing	445,000		444,000
Nonaccrual	103,000	[1]	79,000	[1]
Current and accruing	107,684,000		93,387,000
Total Loans	$ 108,232,000		$ 93,910,000

[1] Approximately $6.0 million and $9.4 million of nonaccrual loans as of March 31, 2013 and December 31, 2012, respectively, are currently performing pursuant to their contractual terms.