Investment Securities (Tables)

9 Months Ended

Sep. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Investment securities available for sale

The amortized cost and fair values of securities available for sale and held to maturity were as follows.

September 30, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	($ in Thousands)
Investment securities available for sale
U. S. Treasury securities	$	1,003	$	—	$	(2	)	$	1,001
Residential mortgage-related securities
FNMA / FHLMC	494,041		12,780		(1,560		)	505,261
GNMA	1,681,380		2,504		(16,048		)	1,667,836
Private-label	1,083		—		(11		)	1,072
GNMA commercial mortgage-related securities	1,539,169		73		(26,165		)	1,513,077
Asset backed securities	108,590		63		(25		)	108,628
Other securities (debt and equity)	4,718		132		(26		)	4,824
Total investment securities available for sale	$	3,829,984	$	15,552	$	(43,837	)	$	3,801,699
Investment securities held to maturity
Obligations of state and political subdivisions (municipal securities)	$	1,192,290	$	14,525	$	(3,858	)	$	1,202,957
Residential mortgage-related securities
FNMA / FHLMC	42,386		464		(404		)	42,446
GNMA	444,196		3,712		(2,615		)	445,293
GNMA commercial mortgage-related securities	554,707		10,250		(11,808		)	553,149
Total investment securities held to maturity	$	2,233,579	$	28,951	$	(18,685	)	$	2,243,845

December 31, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	($ in Thousands)
Investment securities available for sale
U. S. Treasury securities	$	1,000	$	—	$	—		$	1,000
Residential mortgage-related securities
FNMA / FHLMC	625,234		17,298		(2,602		)	639,930
GNMA	2,028,301		1,372		(25,198		)	2,004,475
Private-label	1,134		1		(14		)	1,121
GNMA commercial mortgage-related securities	2,064,508		356		(35,966		)	2,028,898
Other securities (debt and equity)	4,718		105		(21		)	4,802
Total investment securities available for sale	$	4,724,895	$	19,132	$	(63,801	)	$	4,680,226
Investment securities held to maturity
Obligations of state and political subdivisions (municipal securities)	$	1,145,843	$	3,868	$	(12,036	)	$	1,137,675
Residential mortgage-related securities
FNMA / FHLMC	37,697		439		(693		)	37,443
GNMA	89,996		216		(656		)	89,556
Total investment securities held to maturity	$	1,273,536	$	4,523	$	(13,385	)	$	1,264,674

Investment securities held to maturity

The amortized cost and fair values of securities available for sale and held to maturity were as follows.

September 30, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	($ in Thousands)
Investment securities available for sale
U. S. Treasury securities	$	1,003	$	—	$	(2	)	$	1,001
Residential mortgage-related securities
FNMA / FHLMC	494,041		12,780		(1,560		)	505,261
GNMA	1,681,380		2,504		(16,048		)	1,667,836
Private-label	1,083		—		(11		)	1,072
GNMA commercial mortgage-related securities	1,539,169		73		(26,165		)	1,513,077
Asset backed securities	108,590		63		(25		)	108,628
Other securities (debt and equity)	4,718		132		(26		)	4,824
Total investment securities available for sale	$	3,829,984	$	15,552	$	(43,837	)	$	3,801,699
Investment securities held to maturity
Obligations of state and political subdivisions (municipal securities)	$	1,192,290	$	14,525	$	(3,858	)	$	1,202,957
Residential mortgage-related securities
FNMA / FHLMC	42,386		464		(404		)	42,446
GNMA	444,196		3,712		(2,615		)	445,293
GNMA commercial mortgage-related securities	554,707		10,250		(11,808		)	553,149
Total investment securities held to maturity	$	2,233,579	$	28,951	$	(18,685	)	$	2,243,845

December 31, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	($ in Thousands)
Investment securities available for sale
U. S. Treasury securities	$	1,000	$	—	$	—		$	1,000
Residential mortgage-related securities
FNMA / FHLMC	625,234		17,298		(2,602		)	639,930
GNMA	2,028,301		1,372		(25,198		)	2,004,475
Private-label	1,134		1		(14		)	1,121
GNMA commercial mortgage-related securities	2,064,508		356		(35,966		)	2,028,898
Other securities (debt and equity)	4,718		105		(21		)	4,802
Total investment securities available for sale	$	4,724,895	$	19,132	$	(63,801	)	$	4,680,226
Investment securities held to maturity
Obligations of state and political subdivisions (municipal securities)	$	1,145,843	$	3,868	$	(12,036	)	$	1,137,675
Residential mortgage-related securities
FNMA / FHLMC	37,697		439		(693		)	37,443
GNMA	89,996		216		(656		)	89,556
Total investment securities held to maturity	$	1,273,536	$	4,523	$	(13,385	)	$	1,264,674

Amortized cost and fair values of investment securities by contractual maturity

The amortized cost and fair values of investment securities available for sale and held to maturity at September 30, 2017, are shown below. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

	Available for Sale					Held to Maturity
	Amortized Cost		Fair Value			Amortized Cost		Fair Value
	($ in Thousands)
Due in one year or less	$	1,000	$	1,000		$	54,259	$	48,123
Due after one year through five years	4,703		4,675			222,037		227,978
Due after five years through ten years	—		—			281,559		284,789
Due after ten years	—		—			634,435		642,067
Total debt securities	5,703		5,675			1,192,290		1,202,957
Residential mortgage-related securities
FNMA / FHLMC	494,041		505,261			42,386		42,446
GNMA	1,681,380		1,667,836			444,196		445,293
Private-label	1,083		1,072			—		—
GNMA commercial mortgage-related securities	1,539,169		1,513,077			554,707		553,149
Asset backed securities	108,590		108,628			—		—
Equity securities	18		150			—		—
Total investment securities	$	3,829,984	$	3,801,699		$	2,233,579	$	2,243,845
Ratio of Fair Value to Amortized Cost			99.3		%			100.5		%

Realized gains and losses and proceeds from sale

The proceeds from the sale of investment securities for the first nine months ended September 30, 2017 and 2016 are shown below.

	Nine Months Ended September 30,
	2017			2016
	($ in Thousands)
Gross gains on available for sale securities	$	—		$	6,403
Gross gains on held to maturity securities	364			—
Total gains	364			6,403
Gross losses on available for sale securities	—			(202		)
Gross losses on held to maturity securities	(5		)	—
Total losses	(5		)	(202		)
Investment securities gains, net	$	359		$	6,201
Proceeds from sales of investment securities	$	16,059		$	359,591

Unrealized losses and fair value of available for sale and held to maturity securities, by investment category and time length

The following represents gross unrealized losses and the related fair value of investment securities available for sale and held to maturity, aggregated by investment category and length of time individual securities have been in a continuous unrealized loss position, at September 30, 2017.

	Less than 12 months						12 months or more						Total
September 30, 2017	Number of Securities	Unrealized Losses			Fair Value		Number of Securities	Unrealized Losses			Fair Value		Unrealized Losses			Fair Value
	($ in Thousands)
Investment securities available for sale
U.S. Treasury securities	1	$	(2	)	$	1,001	—	$	—		$	—	$	(2	)	$	1,001
Residential mortgage-related securities
FNMA / FHLMC	16	(1,254		)	177,782		2	(306		)	33,842		(1,560		)	211,624
GNMA	22	(9,455		)	687,814		14	(6,593		)	378,457		(16,048		)	1,066,271
Private-label	—	—			—		1	(11		)	1,072		(11		)	1,072
GNMA commercial mortgage-related securities	42	(4,962		)	551,833		56	(21,203		)	891,178		(26,165		)	1,443,011
Asset backed securities	5	(25		)	52,851		—	—			—		(25		)	52,851
Other securities (debt and equity)	1	(26		)	174		—	—			—		(26		)	174
Total	87	$	(15,724	)	$	1,471,455	73	$	(28,113	)	$	1,304,549	$	(43,837	)	$	2,776,004
Investment securities held to maturity
Obligations of state and political subdivisions (municipal securities)	195	$	(1,195	)	$	138,178	108	$	(2,663	)	$	94,432	$	(3,858	)	$	232,610
Residential mortgage-related securities
FNMA / FHLMC	12	(124		)	17,816		4	(280		)	9,910		(404		)	27,726
GNMA	29	(1,628		)	223,379		7	(987		)	67,981		(2,615		)	291,360
GNMA commercial mortgage-related securities	5	(841		)	94,758		19	(10,967		)	427,161		(11,808		)	521,919
Total	241	$	(3,788	)	$	474,131	138	$	(14,897	)	$	599,484	$	(18,685	)	$	1,073,615

For comparative purposes, the following represents gross unrealized losses and the related fair value of investment securities available for sale and held to maturity, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at December 31, 2016.

	Less than 12 months						12 months or more						Total
December 31, 2016	Number of Securities	Unrealized Losses			Fair Value		Number of Securities	Unrealized Losses			Fair Value		Unrealized Losses			Fair Value
	($ in Thousands)
Investment securities available for sale
Residential mortgage-related securities
FNMA / FHLMC	14	$	(2,602	)	$	244,252	—	$	—		$	—	$	(2,602	)	$	244,252
GNMA	54	(25,198		)	1,723,523		—	—			—		(25,198		)	1,723,523
Private-label	—	—			—		1	(14		)	1,119		(14		)	1,119
GNMA commercial mortgage-related securities	74	(16,445		)	1,427,889		21	(19,521		)	429,258		(35,966		)	1,857,147
Other securities (debt and equity)	3	(21		)	1,479		—	—			—		(21		)	1,479
Total	145	$	(44,266	)	$	3,397,143	22	$	(19,535	)	$	430,377	$	(63,801	)	$	3,827,520
Investment securities held to maturity
Obligations of state and political subdivisions (municipal securities)	700	$	(11,937	)	$	414,186	4	$	(99	)	$	1,752	$	(12,036	)	$	415,938
Residential mortgage-related securities
FNMA / FHLMC	14	(441		)	17,477		1	(252		)	6,031		(693		)	23,508
GNMA	39	(656		)	64,633		—	—			—		(656		)	64,633
Total	753	$	(13,034	)	$	496,296	5	$	(351	)	$	7,783	$	(13,385	)	$	504,079