Securities (Tables)

6 Months Ended

Jun. 30, 2013

Investments Debt And Equity Securities [Abstract]

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.

	June 30, 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	$	248,386	$	22,629	$	—	$	271,015	$	248,188	$	29,859	$	—	$	278,047
Residential mortgage-backed securities		10,262		118		109		10,271		10,725		300		—		11,025
States and political subdivisions		2,907,044		8,864		127,843		2,788,065		2,696,468		15,397		4,993		2,706,872
Other		1,000		—		2		998		1,000		—		—		1,000
Total	$	3,166,692	$	31,611	$	127,954	$	3,070,349	$	2,956,381	$	45,556	$	4,993	$	2,996,944
Available for Sale:
U. S. Treasury	$	3,021,080	$	21,643	$	—	$	3,042,723	$	3,020,115	$	37,806	$	—	$	3,057,921
Residential mortgage-backed securities		1,995,296		81,366		1,089		2,075,573		2,382,514		135,514		25		2,518,003
States and political subdivisions		863,754		21,526		6,105		879,175		552,056		39,427		—		591,483
Other		35,899		—		—		35,899		35,892		—		—		35,892
Total	$	5,916,029	$	124,535	$	7,194	$	6,033,370	$	5,990,577	$	212,747	$	25	$	6,203,299

Securities, with Unrealized Losses Segregated by Length of Impairment

As of June 30, 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
Residential mortgage-backed securities	$	7,270	$	109	$	—	$	—	$	7,270	$	109
States and political subdivisions		2,424,783		127,843		—		—		2,424,783		127,843
Other		998		2		—		—		998		2
Total	$	2,433,051	$	127,954	$	—	$	—	$	2,433,051	$	127,954
Available for Sale
Residential mortgage-backed securities	$	87,714	$	1,089	$	—	$	—	$	87,714	$	1,089
States and political subdivisions		338,904		6,105		—		—		338,904		6,105
Total	$	426,618	$	7,194	$	—	$	—	$	426,618	$	7,194

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 June 30, 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	$	24,390	$	24,863	$	1,512,694	$	1,514,523
Due after one year through five years		362,850		389,897		1,577,682		1,600,263
Due after five years through ten years		171,543		167,849		517,090		516,034
Due after ten years		2,597,647		2,477,469		277,368		291,078
Residential mortgage-backed securities		10,262		10,271		1,995,296		2,075,573
Equity securities		—		—		35,899		35,899
Total	$	3,166,692	$	3,070,349	$	5,916,029	$	6,033,370

Sales of Securities Available for Sale

Sales of securities available for sale were as follows:

	Three Months Ended June 30,						Six Months Ended June 30,
	2013			2012			2013			2012
Proceeds from sales	$	3,997,485		$	6,002,402		$	8,495,587		$	15,987,480
Gross realized gains		6			371			11			2,508
Gross realized losses		—			(1	)		—			(2,629	)
Tax (expense) benefit of securities gains/losses		(2	)		(130	)		(4	)		42

Trading Account Securities, at Estimated Fair Value

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

	June 30,		December 31,
	2013		2012
U.S. Treasury	$	14,489	$	14,038
States and political subdivisions		2,288		16,036
Total	$	16,777	$	30,074

Net Gains and Losses on Trading Account Securities

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

	Three Months Ended June  30,						Six Months Ended June  30,
	2013			2012			2013			2012
Net gain on sales transactions	$	282		$	299		$	576		$	622
Net mark-to-market gains (losses)		(377	)		(19	)		(380	)		(79	)
Net gain (loss) on trading account securities	$	(95	)	$	280		$	196		$	543