Securities (Tables)

12 Months Ended

Dec. 31, 2015

Investments, Debt and Equity Securities [Abstract]

Year End Securities Held To Maturity And Available For Sale

Year-end securities held to maturity and available for sale consisted of the following:

	2015								2014
	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	$	249,441	$	7,776	$	—	$	257,217	$	249,009	$	14,604	$	—	$	263,613
Residential mortgage-backed securities	6,456		63		4		6,515		8,012		92		—		8,104
States and political subdivisions	2,405,762		46,003		6,149		2,445,616		2,668,115		34,243		9,035		2,693,323
Other	1,350		—		13		1,337		1,350		—		—		1,350
Total	$	2,663,009	$	53,842	$	6,166	$	2,710,685	$	2,926,486	$	48,939	$	9,035	$	2,966,390
Available for Sale:
U. S. Treasury	$	3,980,986	$	22,041	$	8,507	$	3,994,520	$	3,783,899	$	30,594	$	3,241	$	3,811,252
Residential mortgage-backed securities	1,000,024		42,142		734		1,041,432		1,331,114		68,027		417		1,398,724
States and political subdivisions	3,996,113		133,305		1,459		4,127,959		3,104,563		104,500		156		3,208,907
Other	42,447		—		—		42,447		42,371		—		—		42,371
Total	$	9,019,570	$	197,488	$	10,700	$	9,206,358	$	8,261,947	$	203,121	$	3,814	$	8,461,254

Year End Securities with Unrealized Losses, Segregated by Length of Impairment

Year-end 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
2015
Held to Maturity:
Residential mortgage-backed securities	$	900	$	4	$	—	$	—	$	900	$	4
States and political subdivisions	146,854		1,325		202,423		4,824		349,277		6,149
Other	1,337		13		—		—		1,337		13
Total	$	149,091	$	1,342	$	202,423	$	4,824	$	351,514	$	6,166
Available for Sale:
U.S. Treasury	$	886,087	$	8,507	$	—	$	—	$	886,087	$	8,507
Residential mortgage-backed securities	21,392		212		17,781		522		39,173		734
States and political subdivisions	120,782		1,237		18,485		222		139,267		1,459
Total	$	1,028,261	$	9,956	$	36,266	$	744	$	1,064,527	$	10,700
2014
Held to Maturity:
States and political subdivisions	$	68,024	$	144	$	683,251	$	8,891	$	751,275	$	9,035
Total	$	68,024	$	144	$	683,251	$	8,891	$	751,275	$	9,035
Available for Sale:
U.S. Treasury	$	1,019,230	$	3,241	$	—	$	—	$	1,019,230	$	3,241
Residential mortgage-backed securities	8,550		42		16,944		375		25,494		417
States and political subdivisions	65,751		156		—		—		65,751		156
Total	$	1,093,531	$	3,439	$	16,944	$	375	$	1,110,475	$	3,814

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 December 31, 2015 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	$	161,934	$	163,320	$	793,662	$	796,452
Due after one year through five years	846,629		889,786		2,961,224		2,976,538
Due after five years through ten years	207,488		209,616		1,391,273		1,418,590
Due after ten years	1,440,502		1,441,448		2,830,940		2,930,899
Residential mortgage-backed securities	6,456		6,515		1,000,024		1,041,432
Equity securities	—		—		42,447		42,447
Total	$	2,663,009	$	2,710,685	$	9,019,570	$	9,206,358

Sales of Securities Available for Sale

Sales of securities available for sale were as follows:

	2015			2014			2013
Proceeds from sales	$	12,683,169		$	12,151,287		$	10,056,060
Gross realized gains	228			39			1,206
Gross realized losses	(159		)	(1		)	(30		)
Tax (expense) benefit of securities gains/losses	(24		)	(13		)	(412		)

Premium Amortization and Discount Accretion Included in Income on Securities

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

	2015			2014			2013
Premium amortization	$	(84,467	)	$	(68,070	)	$	(49,112	)
Discount accretion	10,682			6,802			7,191
Net (premium amortization) discount accretion	$	(73,785	)	$	(61,268	)	$	(41,921	)

Year End Trading Account Securities, at Estimated Fair Value

Year-end trading account securities, at estimated fair value, were as follows:

	2015		2014
U.S. Treasury	$	16,443	$	15,339
States and political subdivisions	136		87
Total	$	16,579	$	15,426

Net Gains and Losses on Trading Account Securities

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

	2015			2014		2013
Net gain on sales transactions	$	1,109		$	829	$	878
Net mark-to-market gains (losses)	(53		)	—		(429		)
Net gain on trading account securities	$	1,056		$	829	$	449