Securities Available for Sale and Held to Maturity (Tables)

12 Months Ended

Dec. 31, 2019

Investments Debt And Equity Securities [Abstract]

Amortized Cost and Estimated Fair Value of Available for Sale and Held to Maturity Securities

The following tables are a summary of the amortized cost and estimated fair value of securities available for sale and held to maturity at December 31, 2019 and 2018 ($ in thousands):

	Securities Available for Sale									Securities Held to Maturity
			Gross		Gross			Estimated				Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair		Amortized		Unrealized		Unrealized			Fair
December 31, 2019	Cost		Gains		Losses			Value		Cost		Gains		Losses			Value
U.S. Government agency obligations	$	22,965	$	69	$	(707	)	$	22,327	$	3,781	$	220	$	—		$	4,001
Obligations of states and political    subdivisions		24,952		513		—			25,465		31,781		434		(53	)		32,162
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		69,196		425		(369	)		69,252		10,820		266		(10	)		11,076
Issued by FNMA and FHLMC		714,350		2,171		(3,165	)		713,356		96,631		286		(370	)		96,547
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		656,162		3,777		(1,713	)		658,226		485,324		7,026		(656	)		491,694
Commercial mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		113,359		625		(206	)		113,778		109,762		1,042		(82	)		110,722
Total	$	1,600,984	$	7,580	$	(6,160	)	$	1,602,404	$	738,099	$	9,274	$	(1,171	)	$	746,202
December 31, 2018
U.S. Government agency obligations	$	31,235	$	109	$	(1,009	)	$	30,335	$	3,736	$	78	$	—		$	3,814
Obligations of states and political    subdivisions		50,503		200		(27	)		50,676		35,783		255		(139	)		35,899
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		69,648		147		(2,301	)		67,494		12,090		45		(257	)		11,878
Issued by FNMA and FHLMC		685,520		127		(18,963	)		666,684		115,133		43		(2,887	)		112,289
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		830,129		67		(18,595	)		811,601		578,827		189		(15,441	)		563,575
Commercial mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		187,494		191		(2,662	)		185,023		164,074		299		(2,095	)		162,278
Total	$	1,854,529	$	841	$	(43,557	)	$	1,811,813	$	909,643	$	909	$	(20,819	)	$	889,733

Securities with Gross Unrealized Losses, Segregated by Length of Impairment

The table below includes securities with gross unrealized losses segregated by length of impairment at December 31, 2019 and 2018 ($ in thousands):

	Less than 12 Months					12 Months or More					Total
			Gross					Gross					Gross
	Estimated		Unrealized			Estimated		Unrealized			Estimated		Unrealized
December 31, 2019	Fair Value		Losses			Fair Value		Losses			Fair Value		Losses
U.S. Government agency obligations	$	6,585	$	(105	)	$	12,886	$	(602	)	$	19,471	$	(707	)
Obligations of states and political subdivisions		—		—			6,216		(53	)		6,216		(53	)
Mortgage-backed securities
Residential mortgage pass-through securities
Guaranteed by GNMA		23,544		(107	)		18,529		(272	)		42,073		(379	)
Issued by FNMA and FHLMC		112,879		(230	)		278,120		(3,305	)		390,999		(3,535	)
Other residential mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		158,341		(738	)		151,271		(1,631	)		309,612		(2,369	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		51,312		(167	)		14,155		(121	)		65,467		(288	)
Total	$	352,661	$	(1,347	)	$	481,177	$	(5,984	)	$	833,838	$	(7,331	)
December 31, 2018
U.S. Government agency obligations	$	—	$	—		$	25,045	$	(1,009	)	$	25,045	$	(1,009	)
Obligations of states and political subdivisions		4,954		(9	)		12,802		(157	)		17,756		(166	)
Mortgage-backed securities
Residential mortgage pass-through securities
Guaranteed by GNMA		9,163		(54	)		61,141		(2,504	)		70,304		(2,558	)
Issued by FNMA and FHLMC		31,931		(172	)		731,749		(21,678	)		763,680		(21,850	)
Other residential mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		46,643		(110	)		1,296,221		(33,926	)		1,342,864		(34,036	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		5,497		(37	)		272,789		(4,720	)		278,286		(4,757	)
Total	$	98,188	$	(382	)	$	2,399,747	$	(63,994	)	$	2,497,935	$	(64,376	)

Gains and Losses as a Result of Calls and Disposition of Securities

For the periods presented, gross realized gains or losses as a result of calls and dispositions of securities, as well as any associated proceeds, were as follows ($ in thousands):

	Years Ended December 31,
Available for Sale	2019		2018		2017
Proceeds from calls and sales of securities	$	—	$	—	$	27,682
Gross realized gains		—		—		16
Gross realized losses		—		—		(1	)

Contractual Maturities of Available for Sale and Held to Maturity Securities

The amortized cost and estimated fair value of securities available for sale and held to maturity at December 31, 2019, by contractual maturity, are shown below ($ in thousands).  Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

	Securities				Securities
	Available for Sale				Held to Maturity
	Amortized		Estimated		Amortized		Estimated
	Cost		Fair Value		Cost		Fair Value
Due in one year or less	$	22,480	$	22,623	$	5,071	$	5,115
Due after one year through five years		1,598		1,614		30,491		31,048
Due after five years through ten years		2,561		2,513		—		—
Due after ten years		21,278		21,042		—		—
		47,917		47,792		35,562		36,163
Mortgage-backed securities		1,553,067		1,554,612		702,537		710,039
Total	$	1,600,984	$	1,602,404	$	738,099	$	746,202