Securities (Tables)

12 Months Ended

Dec. 31, 2017

Investments Debt And Equity Securities [Abstract]

Summary of Securities Held for Investment and Securities Available for Sale

The following table summarizes securities held for investment and securities available for sale:

	December 31,
	2017		2016
	(Dollars in thousands)
Held for investment, at cost (fair value: $2,303 and $4,403, respectively)	$	2,292	$	4,365
Available for sale, at fair value		467,703		465,468
Total	$	469,995	$	469,833

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

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

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(Dollars in thousands)
December 31, 2017
Mortgage backed securities (1)	$	187	$	10	$	—		$	197
States and political subdivisions		1,605		3		(2	)		1,606
Other securities		500		—		—			500
Total	$	2,292	$	13	$	(2	)	$	2,303
December 31, 2016
Mortgage backed securities (1)	$	252	$	17	$	—		$	269
States and political subdivisions		3,613		25		(4	)		3,634
Other securities		500		—		—			500
Total	$	4,365	$	42	$	(4	)	$	4,403

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

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

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(Dollars in thousands)
December 31, 2017
U.S. treasuries	$	314,905	$	—	$	(2,103	)	$	312,802
U.S. federal agencies		89,098		82		(329	)		88,851
Mortgage backed securities (1)		18,358		204		(586	)		17,976
States and political subdivisions		41,937		554		(121	)		42,370
Other securities (2)		6,527		71		(894	)		5,704
Total	$	470,825	$	911	$	(4,033	)	$	467,703
December 31, 2016
U.S. treasuries	$	268,763	$	700	$	(920	)	$	268,543
U.S. federal agencies		129,674		373		(405	)		129,642
Mortgage backed securities (1)		19,949		290		(567	)		19,672
States and political subdivisions		40,335		836		(129	)		41,042
Other securities (2)		6,594		125		(150	)		6,569
Total	$	465,315	$	2,324	$	(2,171	)	$	465,468

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

(2) Primarily consists of equity securities.

Maturity of Securities

The maturities of 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,
	2017				2016
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(Dollars in thousands)
Held for Investment
Contractual maturity of debt securities:
Within one year	$	1,036	$	1,034	$	1,561	$	1,568
After one year but within five years		623		627		1,937		1,951
After five years but within ten years		625		633		707		723
After ten years		8		9		160		161
Total	$	2,292	$	2,303	$	4,365	$	4,403
Available for Sale
Contractual maturity of debt securities:
Within one year	$	113,225	$	112,974	$	66,542	$	66,662
After one year but within five years		289,038		287,058		320,150		319,839
After five years but within ten years		6,222		6,500		5,830		6,152
After ten years		55,813		55,467		66,199		66,246
Total debt securities		464,298		461,999		458,721		458,899
Other securities		6,527		5,704		6,594		6,569
Total	$	470,825	$	467,703	$	465,315	$	465,468

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

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

	Year Ended December 31,
	2017		2016		2015
	(Dollarsin thousands)
Proceeds	$	5,412	$	481	$	10,850
Gross gains realized		4,413		227		9,394
Gross losses realized		353		286		125

Company's Book Value of Pledged Securities

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

	Year Ended December 31,
	2017		2016
	(Dollarsin thousands)
Book value of pledged securities	$	440,069	$	439,692

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

The following table summarizes securities with unrealized losses, segregated by the duration of the unrealized loss, at December 31, 2017 and 2016 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, 2017
Held for Investment
Mortgage backed securities	$	—	$	—	$	7	$	—	$	7	$	—
States and political subdivisions		65		—		478		2		543		2
Total	$	65	$	—	$	485	$	2	$	550	$	2
Available for Sale
U.S. treasuries	$	283,302	$	1,653	$	29,500	$	450	$	312,802	$	2,103
U.S. federal agencies		3,499		8		59,220		321		62,719		329
Mortgage backed securities		1		—		14,475		586		14,476		586
States and political subdivisions		21,300		114		585		7		21,885		121
Other securities		1,500		894		—		—		1,500		894
Total	$	309,602	$	2,669	$	103,780	$	1,364	$	413,382	$	4,033
December 31, 2016
Held for Investment
Mortgage backed securities	$	7	$	—	$	9	$	—	$	16	$	—
States and political subdivisions		476		4		—		—		476		4
Total	$	483	$	4	$	9	$	—	$	492	$	4
Available for Sale
U.S. treasuries	$	103,705	$	920	$	—	$	—	$	103,705	$	920
U.S. federal agencies		71,511		357		9,619		48		81,130		405
Mortgage backed securities		3		—		14,834		567		14,837		567
States and political subdivisions		15,289		62		779		67		16,068		129
Other securities		—		—		589		150		589		150
Total	$	190,508	$	1,339	$	25,821	$	832	$	216,329	$	2,171