Securities (Tables)

3 Months Ended

Mar. 31, 2012

Securities [Abstract]

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

	March 31, 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	$	247,893	$	29,275	$	—	$	277,168	$	247,797	$	31,715	$	—	$	279,512
Residential mortgage-backed securities		11,547		178		—		11,725		11,874		153		—		12,027
States and political subdivisions		105,163		7,773		—		112,936		105,325		6,597		—		111,922
Other		1,000		—		—		1,000		1,000		—		—		1,000
Total	$	365,603	$	37,226	$	—	$	402,829	$	365,996	$	38,465	$	—	$	404,461
Available for Sale:
U. S. Treasury	$	3,018,660	$	29,607	$	219	$	3,048,048	$	2,020,621	$	36,111	$	—	$	2,056,732
U.S. government agencies/corporations		250,000		782		—		250,782		250,000		884		—		250,884
Residential mortgage-backed securities		2,967,744		156,222		1		3,123,965		3,135,064		154,386		180		3,289,270
States and political subdivisions		1,942,118		165,320		27		2,107,411		1,996,703		158,133		23		2,154,813
Other		38,009		—		—		38,009		38,001		—		—		38,001
Total	$	8,216,531	$	351,931	$	247	$	8,568,215	$	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
U.S. Treasury	$	250,332	$	219	$	—	$	—	$	250,332	$	219
Residential mortgage-backed securities		16		—		49		1		65		1
States and political subdivisions		2,225		27		—		—		2,225		27
Total	$	252,573	$	246	$	49	$	1	$	252,622	$	247

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	$	14,850	$	15,125
Due after one year through five years		247,893		277,168		3,360,602		3,396,548
Due after five years through ten years		3,320		3,623		208,835		224,491
Due after ten years		101,843		109,313		1,626,491		1,770,077
Residential mortgage-backed securities		11,547		11,725		2,967,744		3,123,965
Equity securities		—		—		38,009		38,009
Total	$	365,603	$	402,829	$	8,216,531	$	8,568,215

Sales Of Securities Available For Sale

	Three Months Ended March 31,
	2012			2011
Proceeds from sales	$	9,985,078		$	5,547,541
Gross realized gains		2,137			9
Gross realized losses		(2,628	)		(4	)
Tax (expense) benefit of securities gains/losses		172			(2	)

Trading Account Securities, At Estimated Fair Value

	March 31,		December 31,
	2012		2011
U.S. Treasury	$	13,409	$	13,609
States and political subdivisions		3,437		—
Total	$	16,846	$	13,609

Net Gains And Losses On Trading Account Securities

	Three Months Ended March 31,
	2012			2011
Net gain on sales transactions	$	323		$	308
Net mark-to-market gains (losses)		(60	)		—
Net gain on trading account securities	$	263		$	308