Securities (Tables)

3 Months Ended

Mar. 31, 2013

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.

	March 31, 2013								December 31, 2012
	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	$	248,286	$	28,433	$	—	$	276,719	$	248,188	$	29,859	$	—	$	278,047
Residential mortgage-backed securities		10,552		304		—		10,856		10,725		300		—		11,025
States and political subdivisions		2,808,170		13,544		30,856		2,790,858		2,696,468		15,397		4,993		2,706,872
Other		1,000		—		7		993		1,000		—		—		1,000
Total	$	3,068,008	$	42,281	$	30,863	$	3,079,426	$	2,956,381	$	45,556	$	4,993	$	2,996,944
Available for Sale:
U. S. Treasury	$	3,020,596	$	35,313	$	—	$	3,055,909	$	3,020,115	$	37,806	$	—	$	3,057,921
Residential mortgage-backed securities		2,182,312		123,611		108		2,305,815		2,382,514		135,514		25		2,518,003
States and political subdivisions		427,345		32,602		45		459,902		552,056		39,427		—		591,483
Other		35,899		—		—		35,899		35,892		—		—		35,892
Total	$	5,666,152	$	191,526	$	153	$	5,857,525	$	5,990,577	$	212,747	$	25	$	6,203,299

Securities, with Unrealized Losses Segregated by Length of Impairment

As of March 31, 2013, securities, with unrealized losses segregated by length of impairment, were as follows:

	Less than 12 Months				More than 12 Months				Total
	Estimated		Unrealized		Estimated		Unrealized		Estimated		Unrealized
	Fair Value		Losses		Fair Value		Losses		Fair Value		Losses
Held to Maturity
States and political subdivisions	$	2,175,897	$	30,856	$	—	$	—	$	2,175,897	$	30,856
Other		993		7		—		—		993		7
Total	$	2,176,890	$	30,863	$	—	$	—	$	2,176,890	$	30,863
Available for Sale
Residential mortgage-backed securities	$	7,668	$	108	$	—	$	—	$	7,668	$	108
States and political subdivisions		4,918		45		—		—		4,918		45
Total	$	12,586	$	153	$	—	$	—	$	12,586	$	153

Amortized Cost and Estimated Fair Value of Securities, Excluding Trading Securities, Presented by Contractual Maturity

The amortized cost and estimated fair value of securities, excluding trading securities, at March 31, 2013 are presented below by contractual maturity. Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations. Residential mortgage-backed securities and equity securities are shown separately since they are not due at a single maturity date.

	Held to Maturity				Available for Sale
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Due in one year or less	$	24,466	$	25,158	$	1,512,771	$	1,516,143
Due after one year through five years		335,997		367,129		1,576,602		1,612,052
Due after five years through ten years		177,104		176,648		77,656		84,092
Due after ten years		2,519,889		2,499,635		280,912		303,524
Residential mortgage-backed securities		10,552		10,856		2,182,312		2,305,815
Equity securities		—		—		35,899		35,899
Total	$	3,068,008	$	3,079,426	$	5,666,152	$	5,857,525

Sales of Securities Available for Sale

Sales of securities available for sale were as follows:

	Three Months Ended March 31,
	2013			2012
Proceeds from sales	$	4,498,102		$	9,985,078
Gross realized gains		5			2,137
Gross realized losses		—			(2,628	)
Tax (expense) benefit of securities gains/losses		(2	)		172

Trading Account Securities, at Estimated Fair Value

Trading account securities, at estimated fair value, were as follows:

	March 31,		December 31,
	2013		2012
U.S. Treasury	$	14,013	$	14,038
States and political subdivisions		8,651		16,036
Total	$	22,664	$	30,074

Net Gains and Losses on Trading Account Securities

Net gains and losses on trading account securities were as follows:

	Three Months Ended March  31,
	2013			2012
Net gain on sales transactions	$	294		$	323
Net mark-to-market gains (losses)		(3	)		(60	)
Net gain on trading account securities	$	291		$	263