Loans and Allowance for Loan Losses, Allowance for Credit Losses (Details) (USD $)	3 Months Ended			12 Months Ended
	Mar. 31, 2013 Loan		Mar. 31, 2012	Dec. 31, 2012
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	$ 69,411,493			$ 69,417,437
Changes in allowance for loan losses [Roll Forward]
Beginning Balance	69,417,000		73,975,000	73,975,000
Charged-off loans	(3,557,313)		(4,925,559)	(19,657,000)
Recovery of previously charged-off loans	1,380,000			9,530,000
Provision for loan losses	2,172,000			5,569,000
Ending Balance	69,411,000			69,417,000
Loans and other extensions of credit granted to directors, executive officers, and their related entities	7,000,000			8,800,000
Amount drawn from loans and other extensions of credit granted	6,400,000			8,100,000
Mortgage loans held-for-sale	30,326,709			41,194,639
Gain loss on sale of loans held for sale	1,800,000		1,500,000
Number of mortgage loans sold to third party	13,650
Mortgage loans sold	3,000,000,000
Number of conventional loans underwritten	3,500
Percentage of loan to value (in hundredths)	80.00%
Number of loans underwritten	2,900
Home equity and consumer mortgage loans	689,500,000
Commercial Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	21,429,000			19,634,000
Changes in allowance for loan losses [Roll Forward]
Beginning Balance	19,634,000		23,397,000	23,397,000
Charged-off loans	(1,513,000)			(4,667,000)
Recovery of previously charged-off loans	15,000			285,000
Provision for loan losses	3,293,000			619,000
Ending Balance	21,429,000			19,634,000
Consumer Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	8,780,000			8,762,000
Changes in allowance for loan losses [Roll Forward]
Beginning Balance	8,762,000		10,302,000	10,302,000
Charged-off loans	(694,000)			(6,731,000)
Recovery of previously charged-off loans	466,000			818,000
Provision for loan losses	246,000			4,373,000
Ending Balance	8,780,000			8,762,000
Construction and Land Development [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	8,992,000			9,164,000
Changes in allowance for loan losses [Roll Forward]
Beginning Balance	9,164,000		12,040,000	12,040,000
Charged-off loans	(24,000)			(2,530,000)
Recovery of previously charged-off loans	127,000			1,155,000
Provision for loan losses	(275,000)			(1,501,000)
Ending Balance	8,992,000			9,164,000
Commercial and Industrial [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	22,814,000			24,738,000
Changes in allowance for loan losses [Roll Forward]
Beginning Balance	24,738,000		20,789,000	20,789,000
Charged-off loans	(1,224,000)			(4,612,000)
Recovery of previously charged-off loans	705,000			7,175,000
Provision for loan losses	(1,405,000)			1,386,000
Ending Balance	22,814,000			24,738,000
Consumer and Other [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	1,444,000			1,094,000
Changes in allowance for loan losses [Roll Forward]
Beginning Balance	1,094,000		1,125,000	1,125,000
Charged-off loans	(103,000)			(1,117,000)
Recovery of previously charged-off loans	67,000			97,000
Provision for loan losses	386,000			989,000
Ending Balance	1,444,000			1,094,000
Unallocated [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	5,952,000			6,025,000
Changes in allowance for loan losses [Roll Forward]
Beginning Balance	6,025,000		6,322,000	6,322,000
Charged-off loans	0			0
Recovery of previously charged-off loans	0			0
Provision for loan losses	(73,000)			(297,000)
Ending Balance	5,952,000			6,025,000
Accruing Loans [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	58,593,000			57,815,000
Accruing Loans [Member] | Commercial Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	18,582,000			16,642,000
Accruing Loans [Member] | Consumer Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	7,236,000			7,336,000
Accruing Loans [Member] | Construction and Land Development [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	8,871,000			8,953,000
Accruing Loans [Member] | Commercial and Industrial [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	22,548,000			23,829,000
Accruing Loans [Member] | Consumer and Other [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	1,356,000			1,055,000
Accruing Loans [Member] | Unallocated [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	0			0
Nonaccrual Loans [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	1,748,000			1,764,000
Nonaccrual Loans [Member] | Commercial Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	571,000			154,000
Nonaccrual Loans [Member] | Consumer Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	852,000			573,000
Nonaccrual Loans [Member] | Construction and Land Development [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	111,000			201,000
Nonaccrual Loans [Member] | Commercial and Industrial [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	174,000			814,000
Nonaccrual Loans [Member] | Consumer and Other [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	40,000			22,000
Nonaccrual Loans [Member] | Unallocated [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	0			0
Troubled Debt Restructurings [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	3,118,000	[1]		3,813,000	[1]
Troubled Debt Restructurings [Member] | Commercial Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	2,276,000	[1]		2,838,000	[1]
Troubled Debt Restructurings [Member] | Consumer Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	692,000	[1]		853,000	[1]
Troubled Debt Restructurings [Member] | Construction and Land Development [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	10,000	[1]		10,000	[1]
Troubled Debt Restructurings [Member] | Commercial and Industrial [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	92,000	[1]		95,000	[1]
Troubled Debt Restructurings [Member] | Consumer and Other [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	48,000	[1]		17,000	[1]
Troubled Debt Restructurings [Member] | Unallocated [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	$ 0	[1]		$ 0	[1]

[1] Troubled debt restructurings of $20.7 million and $27.5 million as of March 31, 2013 and December 31, 2012, respectively, are classified as impaired loans pursuant to U.S. GAAP; however, these loans continue to accrue interest at contractual rates.