Securities (Tables)

9 Months Ended

Sep. 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.

	September 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	$	248,488	$	22,039	$	—	$	270,527	$	248,188	$	29,859	$	—	$	278,047
Residential mortgage-backed securities	9,868		101		57		9,912		10,725		300		—		11,025
States and political subdivisions	2,896,790		8,130		133,446		2,771,474		2,696,468		15,397		4,993		2,706,872
Other	1,000		—		1		999		1,000		—		—		1,000
Total	$	3,156,146	$	30,270	$	133,504	$	3,052,912	$	2,956,381	$	45,556	$	4,993	$	2,996,944
Available for Sale
U.S. Treasury	$	2,521,612	$	22,449	$	—	$	2,544,061	$	3,020,115	$	37,806	$	—	$	3,057,921
Residential mortgage-backed securities	1,828,500		78,336		1,026		1,905,810		2,382,514		135,514		25		2,518,003
States and political subdivisions	1,066,966		22,151		5,105		1,084,012		552,056		39,427		—		591,483
Other	35,908		—		—		35,908		35,892		—		—		35,892
Total	$	5,452,986	$	122,936	$	6,131	$	5,569,791	$	5,990,577	$	212,747	$	25	$	6,203,299

Securities, with Unrealized Losses Segregated by Length of Impairment

As of September 30, 2013, securities, with unrealized losses segregated by length of impairment, were as follows:

	Less than 12 Months				More than 12 Months				Total
	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
Held to Maturity
Residential mortgage-backed securities	$	7,063	$	57	$	—	$	—	$	7,063	$	57
States and political subdivisions	2,342,235		133,446		—		—		2,342,235		133,446
Other	999		1		—		—		999		1
Total	$	2,350,297	$	133,504	$	—	$	—	$	2,350,297	$	133,504
Available for Sale
Residential mortgage-backed securities	$	18,244	$	1,025	$	46	$	1	$	18,290	$	1,026
States and political subdivisions	340,154		5,105		—		—		340,154		5,105
Total	$	358,398	$	6,130	$	46	$	1	$	358,444	$	6,131

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 September 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	$	30,674	$	31,223	$	1,014,141	$	1,015,777
Due after one year through five years	381,844		409,840		1,573,827		1,597,207
Due after five years through ten years	178,783		175,708		669,101		670,434
Due after ten years	2,554,977		2,426,229		331,509		344,655
Residential mortgage-backed securities	9,868		9,912		1,828,500		1,905,810
Equity securities	—		—		35,908		35,908
Total	$	3,156,146	$	3,052,912	$	5,452,986	$	5,569,791

Sales of Securities Available for Sale

Sales of securities available for sale were as follows:

	Three Months Ended   September 30,					Nine Months Ended   September 30,
	2013			2012		2013			2012
Proceeds from sales	$	1,474		$	—	$	8,497,061		$	15,987,480
Gross realized gains	—			—		11			2,508
Gross realized losses	(14		)	—		(14		)	(2,629		)
Tax (expense) benefit of securities gains/losses	5			—		1			42

Trading Account Securities, at Estimated Fair Value

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

	September 30, 2013		December 31, 2012
U.S. Treasury	$	15,289	$	14,038
States and political subdivisions	—		16,036
Total	$	15,289	$	30,074

Net Gains and Losses on Trading Account Securities

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

	Three Months Ended   September 30,					Nine Months Ended   September 30,
	2013			2012		2013			2012
Net gain on sales transactions	$	108		$	310	$	684		$	932
Net mark-to-market gains (losses)	(29		)	22		(409		)	(57		)
Net gain (loss) on trading account securities	$	79		$	332	$	275		$	875