INVESTMENTS

The amortized cost and fair value of investment securities classified as available for sale and held to maturity at December 31, 2016 and 2015, were as follows:



	December 31, 2016
(Dollars in thousands)	Cost		Gross unrealized gains		Gross unrealized losses		Fair value
Investment securities available for sale
U.S. Treasury	$	1,650,675	$	579	$	935	$	1,650,319
Government agency	40,291		107		—		40,398
Mortgage-backed securities	5,259,466		2,809		86,850		5,175,425
Equity securities	71,873		11,634		—		83,507
Corporate bonds	49,367		195		—		49,562
Other	7,615		—		246		7,369
Total investment securities available for sale	$	7,079,287	$	15,324	$	88,031	$	7,006,580

	December 31, 2015
	Cost		Gross unrealized gains		Gross unrealized losses		Fair value
U.S. Treasury	$	1,675,996	$	4	$	1,118	$	1,674,882
Government agency	498,804		230		374		498,660
Mortgage-backed securities	4,692,447		5,120		29,369		4,668,198
Equity securities	7,935		968		10		8,893
Corporate bonds	8,500		—		—		8,500
Other	2,115		45		—		2,160
Total investment securities available for sale	$	6,885,797	$	6,367	$	30,871	$	6,861,293

	December 31, 2016
	Cost		Gross unrealized gains		Gross unrealized losses		Fair value
Investment securities held to maturity
Mortgage-backed securities	$	98	$	6	$	—	$	104

	December 31, 2015
	Cost		Gross unrealized gains		Gross unrealized losses		Fair value
Mortgage-backed securities	$	255	$	10	$	—	$	265

Investments in mortgage-backed securities primarily represent securities issued by the Government National Mortgage Association, Federal National Mortgage Association and Federal Home Loan Mortgage Corporation. Investments in equity securities and corporate bonds represent positions in securities of other financial institutions. The following table provides the amortized cost and fair value by contractual maturity. Expected maturities will differ from contractual maturities on certain securities because borrowers and issuers may have the right to call or prepay obligations with or without prepayment penalties. Repayments of mortgage-backed securities are dependent on the repayments of the underlying loan balances. Equity securities do not have a stated maturity date.



	December 31, 2016				December 31, 2015
(Dollars in thousands)	Cost		Fair value		Cost		Fair value
Investment securities available for sale
Non-amortizing securities maturing in:
One year or less	$	842,798	$	842,947	$	1,255,714	$	1,255,094
One through five years	848,168		847,770		919,086		918,448
Five through 10 years	49,367		49,562		8,500		8,500
Over 10 years	7,615		7,369		2,115		2,160
Mortgage-backed securities	5,259,466		5,175,425		4,692,447		4,668,198
Equity securities	71,873		83,507		7,935		8,893
Total investment securities available for sale	$	7,079,287	$	7,006,580	$	6,885,797	$	6,861,293
Investment securities held to maturity
Mortgage-backed securities held to maturity	$	98	$	104	$	255	$	265

For each period presented, securities gains (losses) include the following:



	Year ended December 31
(Dollars in thousands)	2016			2015			2014
Gross gains on retirement/sales of investment securities available for sale	$	27,104		$	10,834		$	29,129
Gross losses on sales of investment securities available for sale	(431		)	(17		)	(33		)
Total securities gains	$	26,673		$	10,817		$	29,096

The following table provides information regarding securities with unrealized losses as of December 31, 2016 and 2015:



	December 31, 2016
	Less than 12 months				12 months or more				Total
(Dollars in thousands)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Investment securities available for sale:
U.S. Treasury	$	807,822	$	935	$	—	$	—	$	807,822	$	935
Mortgage-backed securities	4,442,700		82,161		362,351		4,689		4,805,051		86,850
Other	7,369		246		—		—		7,369		246
Total	$	5,257,891	$	83,342	$	362,351	$	4,689	$	5,620,242	$	88,031

	December 31, 2015
	Less than 12 months				12 months or more				Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Investment securities available for sale:
U.S. Treasury	$	1,539,637	$	1,118	$	—	$	—	$	1,539,637	$	1,118
Government agency	229,436		374		—		—		229,436		374
Mortgage-backed securities	3,570,470		23,275		280,126		6,094		3,850,596		29,369
Equity securities	728		10		—		—		728		10
Total	$	5,340,271	$	24,777	$	280,126	$	6,094	$	5,620,397	$	30,871

Investment securities with an aggregate fair value of $362.4 million have had continuous unrealized losses for more than 12 months as of December 31, 2016 with an aggregate unrealized loss of $4.7 million. As of December 31, 2016, all 51 of these investments are government sponsored enterprise-issued mortgage-backed securities. None of the unrealized losses identified as of December 31, 2016 or December 31, 2015 relate to the marketability of the securities or the issuer’s ability to honor redemption obligations. For all periods presented, BancShares had the ability and intent to retain these securities for a period of time sufficient to recover all unrealized losses. Therefore, none of the securities were deemed to be other than temporarily impaired.

Investment securities having an aggregate carrying value of $4.55 billion at December 31, 2016 and $4.73 billion at December 31, 2015 were pledged as collateral to secure public funds on deposit and certain short-term borrowings, and for other purposes as required by law.