Investment Securities (Tables)

3 Months Ended

Mar. 31, 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.

March 31, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	($ in Thousands)
Investment securities available for sale:
U. S. Treasury securities	$	1,004	$	1	$	—		$	1,005
Residential mortgage-related securities:
FNMA / FHLMC	575,826		15,710		(1,117		)	590,419
GNMA	2,063,054		1,837		(25,065		)	2,039,826
Private-label	1,118		—		(16		)	1,102
GNMA commercial mortgage-related securities	1,696,287		145		(33,095		)	1,663,337
Other securities (debt and equity)	4,718		94		(11		)	4,801
Total investment securities available for sale	$	4,342,007	$	17,787	$	(59,304	)	$	4,300,490
Investment securities held to maturity:
Obligations of state and political subdivisions (municipal securities)	$	1,131,526	$	7,150	$	(9,479	)	$	1,129,197
Residential mortgage-related securities:
FNMA / FHLMC	38,829		403		(727		)	38,505
GNMA	88,256		146		(762		)	87,640
GNMA commercial mortgage-related securities	296,232		5,005		(6,257		)	294,980
Total investment securities held to maturity	$	1,554,843	$	12,704	$	(17,225	)	$	1,550,322

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.

March 31, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	($ in Thousands)
Investment securities available for sale:
U. S. Treasury securities	$	1,004	$	1	$	—		$	1,005
Residential mortgage-related securities:
FNMA / FHLMC	575,826		15,710		(1,117		)	590,419
GNMA	2,063,054		1,837		(25,065		)	2,039,826
Private-label	1,118		—		(16		)	1,102
GNMA commercial mortgage-related securities	1,696,287		145		(33,095		)	1,663,337
Other securities (debt and equity)	4,718		94		(11		)	4,801
Total investment securities available for sale	$	4,342,007	$	17,787	$	(59,304	)	$	4,300,490
Investment securities held to maturity:
Obligations of state and political subdivisions (municipal securities)	$	1,131,526	$	7,150	$	(9,479	)	$	1,129,197
Residential mortgage-related securities:
FNMA / FHLMC	38,829		403		(727		)	38,505
GNMA	88,256		146		(762		)	87,640
GNMA commercial mortgage-related securities	296,232		5,005		(6,257		)	294,980
Total investment securities held to maturity	$	1,554,843	$	12,704	$	(17,225	)	$	1,550,322

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 March 31, 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
($ in Thousands)	Amortized Cost		Fair Value			Amortized Cost		Fair Value
Due in one year or less	$	3,500	$	3,489		$	41,148	$	32,101
Due after one year through five years	2,204		2,205			252,007		259,468
Due after five years through ten years	—		—			248,861		250,081
Due after ten years	—		—			589,510		587,547
Total debt securities	5,704		5,694			1,131,526		1,129,197
Residential mortgage-related securities:
FNMA / FHLMC	575,826		590,419			38,829		38,505
GNMA	2,063,054		2,039,826			88,256		87,640
Private-label	1,118		1,102			—		—
GNMA commercial mortgage-related securities	1,696,287		1,663,337			296,232		294,980
Equity securities	18		112			—		—
Total investment securities	$	4,342,007	$	4,300,490		$	1,554,843	$	1,550,322
Ratio of Fair Value to Amortized Cost			99.0		%			99.7		%

Realized gains and losses and proceeds from sale

	Three Months Ended March 31,
	2017		2016
	($ in Thousands)
Gross gains	$	—	$	3,287
Gross losses	—		(189		)
Investment securities gains, net	$	—	$	3,098
Proceeds from sales of investment securities	$	—	$	119,379

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 March 31, 2017.

	Less than 12 months						12 months or more						Total
March 31, 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:
Residential mortgage-related securities:
FNMA / FHLMC	13	$	(1,117	)	$	216,103	—	$	—		$	—	$	(1,117	)	$	216,103
GNMA	56	(25,065		)	1,638,688		—	—			—		(25,065		)	1,638,688
Private-label	—	—			—		1	(16		)	1,100		(16		)	1,100
GNMA commercial mortgage-related securities	73	(15,538		)	1,214,494		19	(17,557		)	368,724		(33,095		)	1,583,218
Other securities (debt and equity)	3	(11		)	1,489		—	—			—		(11		)	1,489
Total	145	$	(41,731	)	$	3,070,774	20	$	(17,573	)	$	369,824	$	(59,304	)	$	3,440,598
Investment securities held to maturity:
Municipal securities	538	$	(9,407	)	$	342,534	4	$	(72	)	$	1,778	$	(9,479	)	$	344,312
Residential mortgage-related securities:
FNMA / FHLMC	16	(480		)	19,969		1	(247		)	5,785		(727		)	25,754
GNMA	38	(762		)	62,494		—	—			—		(762		)	62,494
GNMA commercial mortgage-related securities	9	(4,369		)	255,424		2	(1,888		)	39,556		(6,257		)	294,980
Total	601	$	(15,018	)	$	680,421	7	$	(2,207	)	$	47,119	$	(17,225	)	$	727,540

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