Investment Securities (Tables)

6 Months Ended

Jun. 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.

June 30, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	($ in Thousands)
Investment securities available for sale:
U. S. Treasury securities	$	1,004	$	—	$	(2	)	$	1,002
Residential mortgage-related securities:
FNMA / FHLMC	534,058		13,873		(1,406		)	546,525
GNMA	1,729,386		1,894		(17,102		)	1,714,178
Private-label	1,102		—		(16		)	1,086
GNMA commercial mortgage-related securities	1,443,501		74		(23,703		)	1,419,872
Other securities (debt and equity)	4,718		116		(27		)	4,807
Total investment securities available for sale	$	3,713,769	$	15,957	$	(42,256	)	$	3,687,470
Investment securities held to maturity:
Obligations of state and political subdivisions (municipal securities)	$	1,162,920	$	13,766	$	(4,320	)	$	1,172,366
Residential mortgage-related securities:
FNMA / FHLMC	43,575		430		(566		)	43,439
GNMA	473,517		4,048		(3,214		)	474,351
GNMA commercial mortgage-related securities	575,383		8,964		(11,181		)	573,166
Total investment securities held to maturity	$	2,255,395	$	27,208	$	(19,281	)	$	2,263,322

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:
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.

June 30, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	($ in Thousands)
Investment securities available for sale:
U. S. Treasury securities	$	1,004	$	—	$	(2	)	$	1,002
Residential mortgage-related securities:
FNMA / FHLMC	534,058		13,873		(1,406		)	546,525
GNMA	1,729,386		1,894		(17,102		)	1,714,178
Private-label	1,102		—		(16		)	1,086
GNMA commercial mortgage-related securities	1,443,501		74		(23,703		)	1,419,872
Other securities (debt and equity)	4,718		116		(27		)	4,807
Total investment securities available for sale	$	3,713,769	$	15,957	$	(42,256	)	$	3,687,470
Investment securities held to maturity:
Obligations of state and political subdivisions (municipal securities)	$	1,162,920	$	13,766	$	(4,320	)	$	1,172,366
Residential mortgage-related securities:
FNMA / FHLMC	43,575		430		(566		)	43,439
GNMA	473,517		4,048		(3,214		)	474,351
GNMA commercial mortgage-related securities	575,383		8,964		(11,181		)	573,166
Total investment securities held to maturity	$	2,255,395	$	27,208	$	(19,281	)	$	2,263,322

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:
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 available for sale by contractual maturity

The amortized cost and fair values of investment securities available for sale and held to maturity at June 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	$	1,500	$	1,506		$	41,085	$	33,447
Due after one year through five years	4,204		4,175			239,986		246,760
Due after five years through ten years	—		—			261,149		265,255
Due after ten years	—		—			620,700		626,904
Total debt securities	5,704		5,681			1,162,920		1,172,366
Residential mortgage-related securities:
FNMA / FHLMC	534,058		546,525			43,575		43,439
GNMA	1,729,386		1,714,178			473,517		474,351
Private-label	1,102		1,086			—		—
GNMA commercial mortgage-related securities	1,443,501		1,419,872			575,383		573,166
Equity securities	18		128			—		—
Total investment securities	$	3,713,769	$	3,687,470		$	2,255,395	$	2,263,322
Ratio of Fair Value to Amortized Cost			99.3		%			100.4		%

Realized gains and losses and proceeds from sale

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

	Six Months Ended June 30,
	2017			2016
	($ in Thousands)
Gross gains on available for sale securities	$	—		$	6,403
Gross gains on held to maturity securities	361			—
Total gains	361			6,403
Gross losses on available for sale securities	—			(189		)
Gross losses on held to maturity securities	$	(5	)	$	—
Total losses	$	(5	)	$	(189	)
Investment securities gains, net	$	356		$	6,214
Proceeds from sales of investment securities	$	16,059		$	359,484

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 June 30, 2017.

	Less than 12 months						12 months or more						Total
June 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	)	$	1,002	—	$	—		$	—	$	(2	)	$	1,002
Residential mortgage-related securities:
FNMA / FHLMC	18	(1,406		)	223,326		—	—			—		(1,406		)	223,326
GNMA	42	(16,220		)	1,186,468		1	(882		)	35,695		(17,102		)	1,222,163
Private-label	—	—			—		1	(16		)	1,084		(16		)	1,084
GNMA commercial mortgage-related securities	54	(8,627		)	850,180		31	(15,076		)	496,698		(23,703		)	1,346,878
Other securities (debt and equity)	3	(27		)	2,173		—	—			—		(27		)	2,173
Total	118	$	(26,282	)	$	2,263,149	33	$	(15,974	)	$	533,477	$	(42,256	)	$	2,796,626
Investment securities held to maturity:
Municipal securities	301	$	(4,186	)	$	222,642	9	$	(134	)	$	4,814	$	(4,320	)	$	227,456
Residential mortgage-related securities:
FNMA / FHLMC	18	(377		)	25,507		1	(189		)	5,657		(566		)	31,164
GNMA	45	(3,192		)	358,551		1	(22		)	1,246		(3,214		)	359,797
GNMA commercial mortgage-related securities	14	(3,683		)	301,594		10	(7,498		)	241,385		(11,181		)	542,979
Total	378	$	(11,438	)	$	908,294	21	$	(7,843	)	$	253,102	$	(19,281	)	$	1,161,396

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:
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