Investment Securities

A summary of the available-for-sale and held-to-maturity securities portfolios presenting carrying amounts and gross unrealized gains and losses as of December 31, 2015 and 2014 is as follows:



	December 31, 2015									December 31, 2014
(Dollars in thousands)	Amortized Cost		Gross unrealized gains		Gross unrealized losses			Fair Value		Amortized Cost		Gross unrealized gains		Gross unrealized losses			Fair Value
Available-for-sale securities
U.S. Treasury	$	312,282	$	—	$	(5,553	)	$	306,729	$	388,713	$	84	$	(6,992	)	$	381,805
U.S. Government agencies	70,313		198		(275		)	70,236		686,106		4,113		(21,903		)	668,316
Municipal	105,702		3,249		(356		)	108,595		234,951		5,318		(1,740		)	238,529
Corporate notes:
Financial issuers	80,014		1,510		(1,481		)	80,043		129,309		2,006		(1,557		)	129,758
Other	1,500		4		(2		)	1,502		3,766		55		—			3,821
Mortgage-backed: ⁽¹⁾
Mortgage-backed securities	1,069,680		3,834		(21,004		)	1,052,510		271,129		5,448		(4,928		)	271,649
Collateralized mortgage obligations	40,421		172		(506		)	40,087		47,347		249		(535		)	47,061
Equity securities	51,380		5,799		(493		)	56,686		46,592		4,872		(325		)	51,139
Total available-for-sale securities	$	1,731,292	$	14,766	$	(29,670	)	$	1,716,388	$	1,807,913	$	22,145	$	(37,980	)	$	1,792,078
Held-to-maturity securities
U.S. Government agencies	$	687,302	$	4	$	(7,144	)	$	680,162	$	—	$	—	$	—		$	—
Municipal	197,524		867		(442		)	197,949		—		—		—			—
Total held-to-maturity securities	$	884,826	$	871	$	(7,586	)	$	878,111	$	—	$	—	$	—		$	—


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

In 2015, the Company transferred $862.7 million of investment securities with an unrealized loss of $14.4 million from the available-for-sale classification to the held-to-maturity classification. No investment securities were transferred from the available-for-sale classification to the held-to-maturity classification in 2014.

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 December 31, 2015:



	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	$	306,729	$	(5,553	)	$	—	$	—		$	306,729	$	(5,553	)
U.S. Government agencies	56,193		(192		)	8,434		(83		)	64,627		(275		)
Municipal	24,673		(261		)	3,680		(95		)	28,353		(356		)
Corporate notes:
Financial issuers	16,225		(266		)	34,744		(1,215		)	50,969		(1,481		)
Other	998		(2		)	—		—			998		(2		)
Mortgage-backed:
Mortgage-backed securities	835,086		(15,753		)	121,249		(5,251		)	956,335		(21,004		)
Collateralized mortgage obligations	12,782		(189		)	9,196		(317		)	21,978		(506		)
Equity securities	4,896		(77		)	8,485		(416		)	13,381		(493		)
Total available-for-sale securities	$	1,257,582	$	(22,293	)	$	185,788	$	(7,377	)	$	1,443,370	$	(29,670	)
Held-to-maturity securities
U.S. Government agencies	$	450,800	$	(4,223	)	$	235,518	$	(2,921	)	$	686,318	$	(7,144	)
Municipal	51,933		(282		)	29,192		(160		)	81,125		(442		)
Total held-to-maturity securities	$	502,733	$	(4,505	)	$	264,710	$	(3,081	)	$	767,443	$	(7,586	)



	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	$	97,395	$	(31	)	$	193,187	$	(6,961	)	$	290,582	$	(6,992	)
U.S. Government agencies	13,164		(120		)	459,035		(21,783		)	472,199		(21,903		)
Municipal	40,904		(315		)	45,438		(1,425		)	86,342		(1,740		)
Corporate notes:
Financial issuers	1,311		(1		)	57,624		(1,556		)	58,935		(1,557		)
Other	—		—			—		—			—		—
Mortgage-backed:
Mortgage-backed securities	4,875		(60		)	142,301		(4,868		)	147,176		(4,928		)
Collateralized mortgage obligations	13,198		(13		)	14,828		(522		)	28,026		(535		)
Equity securities	—		—			9,462		(325		)	9,462		(325		)
Total available-for-sale securities	$	170,847	$	(540	)	$	921,875	$	(37,440	)	$	1,092,722	$	(37,980	)
Held-to-maturity securities
U.S. Government agencies	$	—	$	—		$	—	$	—		$	—	$	—
Municipal	—		—			—		—			—		—
Total held-to-maturity securities	$	—	$	—		$	—	$	—		$	—	$	—

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 December 31, 2015 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 U.S. government agencies 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 which have a longer duration and maturity.

In 2013, the Company recorded an other-than-temporary impairment charge related to a money market preferred security. The Company recognized this charge because it estimated that it would not be able to recover its amortized basis prior to its anticipated sale of the security as a result of the Volcker Rule.

The following table provides information as to the amount of gross gains and gross losses realized and proceeds received through the sales of available-for-sale investment securities:



	Years Ended December 31,
(Dollars in thousands)	2015			2014			2013
Realized gains	$	658		$	405		$	434
Realized losses	(335		)	(909		)	(106		)
Net realized gains	$	323		$	(504	)	$	328
Other than temporary impairment charges	—			—			(3,328		)
Gains (losses) on available-for-sale securities, net	$	323		$	(504	)	$	(3,000	)
Proceeds from sales of available-for-sale securities, net	$	1,515,559		$	852,330		$	138,274

Net gains on available-for-sale securities resulted in income tax expense of $122,000 in 2015. Net losses on available-for-sale securities resulted in an income tax benefit included in income tax expense of $194,000 and $1.2 million in 2014 and 2013, respectively.

The amortized cost and fair value of securities as of December 31, 2015 and December 31, 2014, 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 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:



	December 31, 2015				December 31, 2014
(Dollars in thousands)	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Available-for-sale securities
Due in one year or less	$	160,856	$	160,756	$	285,596	$	285,889
Due in one to five years	166,550		166,468		172,647		172,885
Due in five to ten years	228,652		225,699		331,389		325,644
Due after ten years	13,753		14,182		653,213		637,811
Mortgage-backed	1,110,101		1,092,597		318,476		318,710
Equity securities	51,380		56,686		46,592		51,139
Total available-for-sale securities	$	1,731,292	$	1,716,388	$	1,807,913	$	1,792,078
Held-to-maturity securities
Due in one year or less	$	—	$	—	$	—	$	—
Due in one to five years	19,208		19,156		—		—
Due in five to ten years	96,454		96,091		—		—
Due after ten years	769,164		762,864		—		—
Total held-to-maturity securities	$	884,826	$	878,111	$	—	$	—

At December 31, 2015 and December 31, 2014, securities having a carrying value of $1.2 billion and $1.1 billion, respectively, were pledged as collateral for public deposits, trust deposits, FHLB advances, securities sold under repurchase agreements and derivatives. At December 31, 2015, there were no securities of a single issuer, other than U.S. Government-sponsored agency securities, which exceeded 10% of shareholders’ equity.