Securities (Tables)

9 Months Ended

Sep. 30, 2014

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, 2014								December 31, 2013
	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	$	248,902	$	15,844	$	—	$	264,746	$	248,592	$	20,139	$	—	$	268,731
Residential mortgage-backed securities	8,445		67		20		8,492		9,674		89		143		9,620
States and political subdivisions	2,683,315		28,822		15,940		2,696,197		2,880,482		7,691		137,861		2,750,312
Other	1,350		—		—		1,350		1,000		—		—		1,000
Total	$	2,942,012	$	44,733	$	15,960	$	2,970,785	$	3,139,748	$	27,919	$	138,004	$	3,029,663
Available for Sale
U.S. Treasury	$	2,892,208	$	16,937	$	889	$	2,908,256	$	2,522,159	$	18,395	$	—	$	2,540,554
U.S. Government agencies/corporations	—		—		—		—		54,024		—		44		53,980
Residential mortgage-backed securities	1,415,433		68,839		661		1,483,611		1,710,664		66,791		1,439		1,776,016
States and political subdivisions	2,388,740		88,047		—		2,476,787		1,476,316		20,090		7,492		1,488,914
Other	42,998		—		—		42,998		35,972		—		—		35,972
Total	$	6,739,379	$	173,823	$	1,550	$	6,911,652	$	5,799,135	$	105,276	$	8,975	$	5,895,436

Securities, with Unrealized Losses Segregated by Length of Impairment

As of September 30, 2014, 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	$	3,242	$	20	$	—	$	—	$	3,242	$	20
States and political subdivisions	87,246		277		985,618		15,663		1,072,864		15,940
Total	$	90,488	$	297	$	985,618	$	15,663	$	1,076,106	$	15,960
Available for Sale
U.S. Treasury	$	247,480	$	889	$	—	$	—	$	247,480	$	889
Residential mortgage-backed securities	7,423		54		17,105		607		24,528		661
Total	$	254,903	$	943	$	17,105	$	607	$	272,008	$	1,550

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, 2014 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	$	124,693	$	127,767	$	787,678	$	791,624
Due after one year through five years	498,817		530,551		1,792,593		1,806,723
Due after five years through ten years	186,813		186,085		1,459,094		1,488,506
Due after ten years	2,123,244		2,117,890		1,241,583		1,298,190
Residential mortgage-backed securities	8,445		8,492		1,415,433		1,483,611
Equity securities	—		—		42,998		42,998
Total	$	2,942,012	$	2,970,785	$	6,739,379	$	6,911,652

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,
	2014			2013			2014			2013
Proceeds from sales	$	3,649,954		$	1,474		$	3,651,982		$	8,497,061
Gross realized gains	33			—			36			11
Gross realized losses	—			(14		)	(1		)	(14		)
Tax (expense) benefit of securities gains/losses	(11		)	5			(12		)	1

Premium Amortization and Discount Accretion Included in Income on Securities [Table Text Block]

Premium amortization and discount accretion included in interest income on securities was as follows:

	Three Months Ended   September 30,						Nine Months Ended   September 30,
	2014			2013			2014			2013
Premium amortization	(17,471		)	(13,526		)	(48,862		)	(34,942		)
Discount accretion	$	1,865		$	1,596		$	4,897		$	4,888
Net (premium amortization) discount accretion	$	(15,606	)	$	(11,930	)	$	(43,965	)	$	(30,054	)

Trading Account Securities, at Estimated Fair Value

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

	September 30, 2014		December 31, 2013
U.S. Treasury	$	15,689	$	15,389
States and political subdivisions	863		1,009
Total	$	16,552	$	16,398

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,
	2014		2013			2014		2013
Net gain on sales transactions	$	167	$	108		$	660	$	684
Net mark-to-market gains (losses)	13		(29		)	10		(409		)
Net gain (loss) on trading account securities	$	180	$	79		$	670	$	275