Investment Securities

The following tables are a summary of the available-for-sale and held-to-maturity securities portfolios as of the dates shown:



	September 30, 2017
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Available-for-sale securities
U.S. Treasury	$	144,872	$	—	$	(727	)	$	144,145
U.S. Government agencies	159,884		10		(566		)	159,328
Municipal	113,796		2,493		(273		)	116,016
Corporate notes:
Financial issuers	60,325		63		(771		)	59,617
Other	1,000		—		(3		)	997
Mortgage-backed: ⁽¹⁾
Mortgage-backed securities	1,114,655		1,477		(30,436		)	1,085,696
Collateralized mortgage obligations	63,934		230		(412		)	63,752
Equity securities	33,166		3,867		(681		)	36,352
Total available-for-sale securities	$	1,691,632	$	8,140	$	(33,869	)	$	1,665,903
Held-to-maturity securities
U.S. Government agencies	$	585,061	$	249	$	(12,579	)	$	572,731
Municipal	234,279		2,185		(2,159		)	234,305
Total held-to-maturity securities	$	819,340	$	2,434	$	(14,738	)	$	807,036



	December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Available-for-sale securities
U.S. Treasury	$	142,741	$	1	$	(759	)	$	141,983
U.S. Government agencies	189,540		47		(435		)	189,152
Municipal	129,446		2,969		(606		)	131,809
Corporate notes:
Financial issuers	65,260		132		(1,000		)	64,392
Other	1,000		—		(1		)	999
Mortgage-backed: ⁽¹⁾
Mortgage-backed securities	1,185,448		284		(54,330		)	1,131,402
Collateralized mortgage obligations	30,105		67		(490		)	29,682
Equity securities	32,608		3,429		(789		)	35,248
Total available-for-sale securities	$	1,776,148	$	6,929	$	(58,410	)	$	1,724,667
Held-to-maturity securities
U.S. Government agencies	$	433,343	$	7	$	(24,470	)	$	408,880
Municipal	202,362		647		(4,287		)	198,722
Total held-to-maturity securities	$	635,705	$	654	$	(28,757	)	$	607,602



	September 30, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Available-for-sale securities
U.S. Treasury	$	30,017	$	19	$	—		$	30,036
U.S. Government agencies	93,561		163		(41		)	93,683
Municipal	106,033		3,395		(147		)	109,281
Corporate notes:
Financial issuers	65,215		299		(1,311		)	64,203
Other	1,000		—		—			1,000
Mortgage-backed: ⁽¹⁾
Mortgage-backed securities	1,257,070		7,958		(54		)	1,264,974
Collateralized mortgage obligations	35,935		304		(102		)	36,137
Equity securities	48,568		2,998		(784		)	50,782
Total available-for-sale securities	$	1,637,399	$	15,136	$	(2,439	)	$	1,650,096
Held-to-maturity securities
U.S. Government agencies	$	729,417	$	7,577	$	(2,879	)	$	734,115
Municipal	203,350		5,515		(314		)	208,551
Total held-to-maturity securities	$	932,767	$	13,092	$	(3,193	)	$	942,666


(1)	Consisting entirely of residential mortgage-backed securities, none of which are subprime.

The following table presents the portion of the Company’s available-for-sale and held-to-maturity securities portfolios which has gross unrealized losses, reflecting the length of time that individual securities have been in a continuous unrealized loss position at September 30, 2017:



	Continuous unrealized losses existing for less than 12 months					Continuous unrealized losses existing for greater than 12 months					Total
(Dollars in thousands)	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Available-for-sale securities
U.S. Treasury	$	144,144	$	(727	)	$	—	$	—		$	144,144	$	(727	)
U.S. Government agencies	112,268		(451		)	41,980		(115		)	154,248		(566		)
Municipal	24,117		(138		)	10,725		(135		)	34,842		(273		)
Corporate notes:
Financial issuers	—		—			35,194		(771		)	35,194		(771		)
Other	—		—			997		(3		)	997		(3		)
Mortgage-backed:
Mortgage-backed securities	51,035		(6,629		)	798,152		(23,807		)	849,187		(30,436		)
Collateralized mortgage obligations	25,685		(195		)	7,216		(217		)	32,901		(412		)
Equity securities	9,177		(283		)	6,102		(398		)	15,279		(681		)
Total available-for-sale securities	$	366,426	$	(8,423	)	$	900,366	$	(25,446	)	$	1,266,792	$	(33,869	)
Held-to-maturity securities
U.S. Government agencies	$	400,980	$	(12,579	)	$	—	$	—		$	400,980	$	(12,579	)
Municipal	115,384		(2,159		)	—		—			115,384		(2,159		)
Total held-to-maturity securities	$	516,364	$	(14,738	)	$	—	$	—		$	516,364	$	(14,738	)

The Company conducts a regular assessment of its investment securities to determine whether securities are other-than-temporarily impaired considering, among other factors, the nature of the securities, credit ratings or financial condition of the issuer, the extent and duration of the unrealized loss, expected cash flows, market conditions and the Company’s ability to hold the securities through the anticipated recovery period.

The Company does not consider securities with unrealized losses at September 30, 2017 to be other-than-temporarily impaired. The Company does not intend to sell these investments and it is more likely than not that the Company will not be required to sell these investments before recovery of the amortized cost bases, which may be the maturity dates of the securities. The unrealized losses within each category have occurred as a result of changes in interest rates, market spreads and market conditions subsequent to purchase. Securities with continuous unrealized losses existing for more than twelve months were primarily corporate notes and mortgage-backed securities. Unrealized losses recognized on corporate notes and mortgage-backed securities are the result of increases in yields for similar types of securities.

The following table provides information as to the amount of gross gains and gross losses realized and proceeds received through the sale or call of investment securities:



	Three months ended September 30,						Nine months ended September 30,
(Dollars in thousands)	2017			2016			2017			2016
Realized gains	$	58		$	3,429		$	106		$	7,466
Realized losses	(19		)	(124		)	(75		)	(1,396		)
Net realized gains	$	39		$	3,305		$	31		$	6,070
Other than temporary impairment charges	—			—			—			—
Gains on investment securities, net	$	39		$	3,305		$	31		$	6,070
Proceeds from sales and calls of available-for-sale securities	$	136,789		$	1,114,666		$	146,518		$	2,186,662
Proceeds from calls of held-to-maturity securities	17			141,885			51,079			423,866

The amortized cost and fair value of securities as of September 30, 2017, December 31, 2016 and September 30, 2016, by contractual maturity, are shown in the following table. Contractual maturities may differ from actual maturities as borrowers may have the right to call or repay obligations with or without call or prepayment penalties. Mortgage-backed securities determined to be available-for-sale are not included in the maturity categories in the following maturity summary as actual maturities may differ from contractual maturities because the underlying mortgages may be called or prepaid without penalties:



	September 30, 2017				December 31, 2016				September 30, 2016
(Dollars in thousands)	Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value
Available-for-sale securities
Due in one year or less	$	150,907	$	150,241	$	145,353	$	145,062	$	115,227	$	115,487
Due in one to five years	282,443		282,121		321,019		320,423		141,364		141,368
Due in five to ten years	38,339		39,458		27,319		28,451		28,696		31,319
Due after ten years	8,188		8,283		34,296		34,399		10,539		10,029
Mortgage-backed	1,178,589		1,149,448		1,215,553		1,161,084		1,293,005		1,301,111
Equity securities	33,166		36,352		32,608		35,248		48,568		50,782
Total available-for-sale securities	$	1,691,632	$	1,665,903	$	1,776,148	$	1,724,667	$	1,637,399	$	1,650,096
Held-to-maturity securities
Due in one year or less	$	170	$	171	$	—	$	—	$	—	$	—
Due in one to five years	36,914		36,734		29,794		29,416		25,927		26,023
Due in five to ten years	193,387		192,581		69,664		67,820		64,835		65,842
Due after ten years	588,869		577,550		536,247		510,366		842,005		850,801
Total held-to-maturity securities	$	819,340	$	807,036	$	635,705	$	607,602	$	932,767	$	942,666

Securities having a fair value of $1.6 billion at September 30, 2017 as well as securities having a fair value of $1.4 billion at December 31, 2016 and September 30, 2016 were pledged as collateral for public deposits, trust deposits, Federal Home Loan Bank ("FHLB") advances, securities sold under repurchase agreements and derivatives. At September 30, 2017, there were no securities of a single issuer, other than U.S. Government-sponsored agency securities, which exceeded 10% of shareholders’ equity.