Securities (Tables)

12 Months Ended

Dec. 31, 2015

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,
	2015		2014
	(Dollars in thousands)
Held for investment, at cost (fair value: $8,850 and $8,671, respectively)	$	8,789	$	8,593
Available for sale, at fair value		544,160		516,190
Total	$	552,949	$	524,783

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, 2015
Mortgage backed securities (1)	$	347	$	25	$	—	$	372
States and political subdivisions		8,442		36		—		8,478
Total	$	8,789	$	61	$	—	$	8,850
December 31, 2014
Mortgage backed securities (1)	$	471	$	34	$	—	$	505
States and political subdivisions		8,122		44		—		8,166
Total	$	8,593	$	78	$	—	$	8,671

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, 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
December 31, 2014
U.S. treasuries	$	248,767	$	404	$	(178	)	$	248,993
U.S. federal agencies		171,641		983		(175	)		172,449
Mortgage backed securities (1)		26,441		602		(586	)		26,457
States and political subdivisions		51,706		1,716		(49	)		53,373
Other securities (2)		10,798		4,252		(132	)		14,918
Total	$	509,353	$	7,957	$	(1,120	)	$	516,190

(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,
	2015				2014
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(Dollars in thousands)
Held for Investment
Contractual maturity of debt securities:
Within one year	$	5,168	$	5,174	$	1,451	$	1,456
After one year but within five years		2,800		2,829		6,603		6,642
After five years but within ten years		795		319		380		396
After ten years		26		528		159		177
Total	$	8,789	$	8,850	$	8,593	$	8,671
Available for Sale
Contractual maturity of debt securities:
Within one year	$	272,820	$	272,779	$	41,772	$	41,870
After one year but within five years		178,617		180,145		350,975		352,044
After five years but within ten years		8,483		9,075		21,990		22,717
After ten years		75,522		75,853		87,252		88,132
Total debt securities		535,442		537,852		501,989		504,763
Equity securities		6,228		6,308		7,364		11,427
Total	$	541,670	$	544,160	$	509,353	$	516,190

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,
	2015		2014		2013
	(Dollarsin thousands)
Proceeds	$	10,850	$	4,855	$	521
Gross gains realized		9,394		1,641		456
Gross losses realized		125		—		36

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,
	2015		2014
	(Dollarsin thousands)
Book value of pledged securities	$	493,540	$	522,190

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, 2015 and 2014 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, 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
December 31, 2014
Held for Investment
Mortgage backed securities	$	—	$	—	$	—	$	—	$	—	$	—
States and political subdivisions		—		—		—		—		—		—
Total	$	—	$	—	$	—	$	—	$	—	$	—
Available for Sale
U.S. treasuries	$	149,589	$	178	$	—	$	—	$	149,589	$	178
U.S. federal agencies		40,551		113		13,653		62		54,204		175
Mortgage backed securities		17,041		585		26		1		17,067		586
States and political subdivisions		3,093		26		977		23		4,070		49
Other securities		—		—		300		132		300		132
Total	$	210,274	$	902	$	14,956	$	218	$	225,230	$	1,120