Securities (Tables)

12 Months Ended

Dec. 31, 2016

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,
	2016		2015
	(Dollars in thousands)
Held for investment, at cost (fair value: $4,403 and $8,850, respectively)	$	4,365	$	8,789
Available for sale, at fair value		465,468		544,160
Total	$	469,833	$	552,949

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, 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
December 31, 2015
Mortgage backed securities (1)	$	347	$	25	$	—		$	372
States and political subdivisions		7,942		36		—			7,978
Other securities		500		—		—			500
Total	$	8,789	$	61	$	—		$	8,850

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, 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
December 31, 2015
U.S. treasuries	$	328,965	$	776	$	(45	)	$	329,696
U.S. federal agencies		131,522		527		(153	)		131,896
Mortgage backed securities (1)		21,973		425		(543	)		21,855
States and political subdivisions		49,521		1,447		(48	)		50,920
Other securities (2)		9,689		249		(145	)		9,793
Total	$	541,670	$	3,424	$	(934	)	$	544,160

(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,
	2016				2015
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(Dollars in thousands)
Held for Investment
Contractual maturity of debt securities:
Within one year	$	1,561	$	1,568	$	5,168	$	5,174
After one year but within five years		1,937		1,951		2,800		2,829
After five years but within ten years		707		723		795		319
After ten years		160		161		26		528
Total	$	4,365	$	4,403	$	8,789	$	8,850
Available for Sale
Contractual maturity of debt securities:
Within one year	$	66,542	$	66,662	$	272,820	$	272,779
After one year but within five years		320,150		319,839		178,617		180,145
After five years but within ten years		5,830		6,152		8,483		9,075
After ten years		66,199		66,246		75,522		75,853
Total debt securities		458,721		458,899		535,442		537,852
Other securities		6,594		6,569		6,228		6,308
Total	$	465,315	$	465,468	$	541,670	$	544,160

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,
	2016		2015		2014
	(Dollarsin thousands)
Proceeds	$	481	$	10,850	$	4,855
Gross gains realized		227		9,394		1,641
Gross losses realized		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,
	2016		2015
	(Dollarsin thousands)
Book value of pledged securities	$	439,692	$	493,540

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, 2016 and 2015 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, 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
December 31, 2015
Held for Investment
Mortgage backed securities	$	21	$	—	$	—	$	—	$	21	$	—
States and political subdivisions		—		—		—		—		—		—
Total	$	21	$	—	$	—	$	—	$	21	$	—
Available for Sale
U.S. treasuries	$	139,762	$	45	$	—	$	—	$	139,762	$	45
U.S. federal agencies		46,948		118		5,969		35		52,917		153
Mortgage backed securities		59		—		14,844		543		14,903		543
States and political subdivisions		1,932		47		245		1		2,177		48
Other securities		304		142		105		3		409		145
Total	$	189,005	$	352	$	21,163	$	582	$	210,168	$	934