Securities (Tables)

9 Months Ended

Sep. 30, 2012

Amortized Cost And Estimated Fair Value Of Securities, Excluding Trading Securities

A summary of the amortized cost and estimated fair value of securities, excluding trading securities, is presented below.

	September 30, 2012								December 31, 2011
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Held to Maturity
U. S. Treasury	$	248,088	$	31,892	$	—	$	279,980	$	247,797	$	31,715	$	—	$	279,512
Residential mortgage-backed securities		11,074		360		—		11,434		11,874		153		—		12,027
States and political subdivisions		104,835		12,009		—		116,844		105,325		6,597		—		111,922
Other		1,000		—		—		1,000		1,000		—		—		1,000
Total	$	364,997	$	44,261	$	—	$	409,258	$	365,996	$	38,465	$	—	$	404,461
Available for Sale:
U. S. Treasury	$	3,019,622	$	41,930	$	—	$	3,061,552	$	2,020,621	$	36,111	$	—	$	2,056,732
U.S. government agencies/corporations		250,000		145		—		250,145		250,000		884		—		250,884
Residential mortgage-backed securities		2,587,218		164,665		—		2,751,883		3,135,064		154,386		180		3,289,270
States and political subdivisions		2,412,514		205,676		12		2,618,178		1,996,703		158,133		23		2,154,813
Other		35,887		—		—		35,887		38,001		—		—		38,001
Total	$	8,305,241	$	412,416	$	12	$	8,717,645	$	7,440,389	$	349,514	$	203	$	7,789,700

Securities, With Unrealized Losses Segregated By Length Of Impairment

	Less than 12 Months				More than 12 Months				Total
	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
Available for Sale
States and political subdivisions	$	16,761	$	12	$	—	$	—	$	16,761	$	12

Amortized Cost And Estimated Fair Value Of Securities, Excluding Trading Securities, Presented By Contractual Maturity

	Held to Maturity				Available for Sale
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Due in one year or less	$	1,000	$	1,000	$	635,154	$	638,634
Due after one year through five years		248,088		279,980		2,900,392		2,949,445
Due after five years through ten years		3,301		3,672		215,664		234,329
Due after ten years		101,534		113,172		1,930,926		2,107,467
Residential mortgage-backed securities		11,074		11,434		2,587,218		2,751,883
Equity securities		—		—		35,887		35,887
Total	$	364,997	$	409,258	$	8,305,241	$	8,717,645

Sales Of Securities Available For Sale

	Three Months Ended September 30,					Nine Months Ended September 30,
	2012		2011			2012			2011
Proceeds from sales	$	—	$	39,005		$	15,987,480		$	5,587,391
Gross realized gains		—		6,409			2,508			6,418
Gross realized losses		—		—			(2,629	)		4
Tax (expense) benefit of securities gains/losses		—		(2,243	)		42			(2,245	)

Trading Account Securities, At Estimated Fair Value

	September 30, 2012		December 31, 2011
U.S. Treasury	$	13,761	$	13,609
States and political subdivisions		1,062		—
Total	$	14,823	$	13,609

Net Gains And Losses On Trading Account Securities

	Three Months Ended September 30,				Nine Months Ended September 30,
	2012		2011		2012			2011
Net gain on sales transactions	$	310	$	303	$	932		$	772
Net mark-to-market gains (losses)		22		4		(57	)		11
Net gain on trading account securities	$	332	$	307	$	875		$	783