Securities (Tables)

12 Months Ended

Dec. 31, 2019

Investments Debt And Equity Securities [Abstract]

Summary of Amortized Cost and Estimated Fair Values of Debt Securities Held for Investment

The following table summarizes the amortized cost and estimated fair values of debt securities held for investment:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(Dollars in thousands)
December 31, 2019
Mortgage backed securities (1)	$	93	$	4	$	—		$	97
States and political subdivisions		1,310		1		(5	)		1,306
Other securities		500		—		—			500
Total	$	1,903	$	5	$	(5	)	$	1,903
December 31, 2018
Mortgage backed securities (1)	$	133	$	5	$	—		$	138
States and political subdivisions		795		—		—			795
Other securities		500		—		—			500
Total	$	1,428	$	5	$	—		$	1,433

Summary of Amortized Cost and Estimated Fair Values of Debt Securities Available for Sale

The following table summarizes the amortized cost and estimated fair values of debt securities available for sale:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(Dollars in thousands)
December 31, 2019
U.S. treasuries	$	409,488	$	4,974	$	(13	)	$	414,449
U.S. federal agencies		23,039		23		(38	)		23,024
Mortgage backed securities (1)		16,941		128		(64	)		17,005
States and political subdivisions		22,294		282		(45	)		22,531
Asset backed securities		13,320		—		(606	)		12,714
Total	$	485,082	$	5,407	$	(766	)	$	489,723
December 31, 2018
U.S. treasuries	$	699,882	$	1,108	$	(3,524	)	$	697,466
U.S. federal agencies		30,079		—		(161	)		29,918
Mortgage backed securities (1)		2,352		114		—			2,466
States and political subdivisions		27,246		277		(112	)		27,411
Asset backed securities		14,015		—		(572	)		13,443
Total	$	773,574	$	1,499	$	(4,369	)	$	770,704

(1) Primarily consists of FHLMC, FNMA, GNMA and mortgage backed securities through U.S. agencies.

Maturity of Debt Securities

The maturities of debt securities held for investment and available for sale are summarized in the following table using contractual maturities. Actual maturities may differ from contractual maturities due to obligations that are called or prepaid. For purposes of the maturity table, mortgage-backed securities, which are not due at a single maturity date, have been presented at their contractual maturity.

	December 31,
	2019				2018
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(Dollars in thousands)
Held for Investment
Contractual maturity of debt securities:
Within one year	$	300	$	300	$	495	$	495
After one year but within five years		1,058		1,055		369		370
After five years but within ten years		543		546		562		565
After ten years		2		2		2		3
Total	$	1,903	$	1,903	$	1,428	$	1,433
Available for Sale
Contractual maturity of debt securities:
Within one year	$	186,373	$	186,539	$	411,256	$	410,327
After one year but within five years		252,519		257,430		313,416		311,924
After five years but within ten years		5,873		6,008		7,524		7,685
After ten years		40,317		39,746		41,378		40,768
Total debt securities	$	485,082	$	489,723	$	773,574	$	770,704

Proceeds from Sales and Realized Securities Losses, on Available for Sale Debt Securities

The following is a detail of proceeds from sales and realized securities losses, on available for sale debt securities:

	Year Ended December 31,
	2019		2018		2017
	(Dollars in thousands)
Proceeds	$	—	$	31,285	$	—
Gross losses realized		—		109		—

Company's Book Value of Pledged Debt Securities

The following table is a summary of the Company’s book value of debt securities that were pledged as collateral for public funds on deposit, repurchase agreements and for other purposes as required or permitted by law:

	December 31,
	2019		2018
	(Dollars in thousands)
Book value of pledged securities	$	445,702	$	472,053

Summary of Debt Securities with Unrealized Losses, Segregated by Duration of Unrealized Loss

The following table summarizes debt securities with unrealized losses, segregated by the duration of the unrealized loss, at December 31, 2019 and 2018 respectively:

	Less than 12 Months				More than 12 Months				Total
	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
	(Dollars in thousands)
December 31, 2019
Held for Investment
Mortgage backed securities	$	—	$	—	$	3	$	—	$	3	$	—
States and political subdivisions		1,016		5		—		—		1,016		5
Total	$	1,016	$	5	$	3	$	—	$	1,019	$	5
Available for Sale
U.S. treasuries	$	8,999	$	10	$	19,988	$	3	$	28,987	$	13
U.S. federal agencies		10,362		19		2,700		19		13,062		38
Mortgage backed securities		15,165		64		—		—		15,165		64
States and political subdivisions		3,890		45		—		—		3,890		45
Asset backed securities		—		—		12,714		606		12,714		606
Total	$	38,416	$	138	$	35,402	$	628	$	73,818	$	766
December 31, 2018
Held for Investment
Mortgage backed securities	$	—	$	—	$	4	$	—	$	4	$	—
Total	$	—	$	—	$	4	$	—	$	4	$	—
Available for Sale
U.S. treasuries	$	296,438	$	90	$	261,639	$	3,434	$	558,077	$	3,524
U.S. federal agencies		1,705		7		27,035		154		28,740		161
Mortgage backed securities		1		—		1		—		2		—
States and political subdivisions		1,593		3		11,527		109		13,120		112
Asset backed securities		—		—		13,443		572		13,443		572
Total	$	299,737	$	100	$	313,645	$	4,269	$	613,382	$	4,369