INVESTMENT SECURITIES

The amortized cost and fair values of investment securities, with gross unrealized gains and losses, consist of the following:



	December 31, 2016
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Securities available for sale:
U.S. Government-sponsored enterprise obligations	$	212,662	$	245	$	(549	)	$	212,358
Obligations of state and political subdivisions	286,458		1,948		(5,207		)	283,199
Mortgage-backed securities	2,888,180		4,820		(41,291		)	2,851,709
Other securities	98,974		361		(504		)	98,831
Total securities available for sale	$	3,486,274	$	7,374	$	(47,551	)	$	3,446,097
Securities held to maturity:
Obligations of state and political subdivisions	$	64,726	$	1,609	$	(133	)	$	66,202
Mortgage-backed securities	24,490		57		(817		)	23,730
Total securities held to maturity	$	89,216	$	1,666	$	(950	)	$	89,932



	December 31, 2015
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Securities available for sale:
U.S. Government-sponsored enterprise obligations	$	252,514	$	1,161	$	(1,592	)	$	252,083
Obligations of state and political subdivisions	182,541		5,429		(9		)	187,961
Mortgage-backed securities	2,272,879		8,457		(16,523		)	2,264,813
Other securities	95,496		430		(497		)	95,429
Total securities available for sale	$	2,803,430	$	15,477	$	(18,621	)	$	2,800,286
Securities held to maturity:
Obligations of state and political subdivisions	$	69,979	$	2,803	$	(101	)	$	72,681
Mortgage-backed securities	28,949		107		(776		)	28,280
Total securities held to maturity	$	98,928	$	2,910	$	(877	)	$	100,961

Securities with carrying values of $1.5 billion and $1.4 billion were pledged to secure public deposits and other borrowings at December 31, 2016 and 2015, respectively.

Information pertaining to securities with gross unrealized losses, aggregated by investment category and length of time that individual securities have been in a continuous loss position, is as follows:



	December 31, 2016
	Less Than Twelve Months					Over Twelve Months					Total
(Dollars in thousands)	Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value
Securities available for sale:
U.S. Government-sponsored enterprise obligations	$	(549	)	$	150,554	$	—		$	—	$	(549	)	$	150,554
Obligations of state and political obligations	(5,207		)	148,059		—			—		(5,207		)	148,059
Mortgage-backed securities	(38,667		)	2,191,563		(2,624		)	98,912		(41,291		)	2,290,475
Other Securities	(451		)	36,484		(53		)	3,850		(504		)	40,334
Total securities available for sale	$	(44,874	)	$	2,526,660	$	(2,677	)	$	102,762	$	(47,551	)	$	2,629,422

Securities held to maturity:
Obligations of state and political obligations	$	(133	)	$	10,602	$	—		$	—	$	(133	)	$	10,602
Mortgage-backed securities	(330		)	12,288		(487		)	10,960		(817		)	23,248
Total securities held to maturity	$	(463	)	$	22,890	$	(487	)	$	10,960	$	(950	)	$	33,850



	December 31, 2015
	Less Than Twelve Months					Over Twelve Months					Total
(Dollars in thousands)	Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value
Securities available for sale:
U.S. Government-sponsored enterprise obligations	$	(1,214	)	$	177,839	$	(378	)	$	28,116	$	(1,592	)	$	205,955
Obligations of state and political obligations	(9		)	5,765		—			—		(9		)	5,765
Mortgage-backed securities	(11,737		)	1,279,914		(4,786		)	185,215		(16,523		)	1,465,129
Other Securities	(488		)	51,975		(9		)	499		(497		)	52,474
Total securities available for sale	$	(13,448	)	$	1,515,493	$	(5,173	)	$	213,830	$	(18,621	)	$	1,729,323

Securities held to maturity:
Obligations of state and political obligations	$	(9	)	$	1,999	$	(92	)	$	4,162	$	(101	)	$	6,161
Mortgage-backed securities	(45		)	3,530		(731		)	17,573		(776		)	21,103
Total securities held to maturity	$	(54	)	$	5,529	$	(823	)	$	21,735	$	(877	)	$	27,264

The Company assessed the nature of the unrealized losses in its portfolio as of December 31, 2016 and 2015 to determine if there are losses that should be deemed other-than-temporary. In its analysis of these securities, management considered numerous factors to determine whether there were instances where the amortized cost basis of the debt securities would not be fully recoverable, including, but not limited to:


•	The length of time and extent to which the estimated fair value of the securities was less than their amortized cost,


•	Whether adverse conditions were present in the operations, geographic area, or industry of the issuer,


•	The payment structure of the security, including scheduled interest and principal payments, including the issuer’s failures to make scheduled payments, if any, and the likelihood of failure to make scheduled payments in the future,


•	Changes to the rating of the security by a rating agency, and


•	Subsequent recoveries or additional declines in fair value after the balance sheet date.

Management believes it has considered these factors, as well as all relevant information available, when determining the expected future cash flows of the securities in question. In each instance, management has determined the cost basis of the securities would be fully recoverable. Management also has the intent to hold debt securities until their maturity or anticipated recovery if the security is classified as available for sale. In addition, management does not believe the Company will be required to sell debt securities before the anticipated recovery of the amortized cost basis of the security. As a result of the Company's analysis, no declines in the estimated fair value of the Company's investment securities were deemed to be other-than-temporary at December 31, 2016 or 2015.

At December 31, 2016, 397 debt securities had unrealized losses of 1.79% of the securities’ amortized cost basis. At December 31, 2015, 252 debt securities had unrealized losses of 1.10% of the securities’ amortized cost basis. The unrealized losses for each of the securities related to market interest rate changes and not credit concerns of the issuers. Additional information on securities that have been in a continuous loss position for over twelve months at December 31 is presented in the following table.



(Dollars in thousands)	2016		2015
Number of securities
Issued by Fannie Mae, Freddie Mac, or Ginnie Mae	28		40
Issued by political subdivisions	—		2
Other	3		1
	31		43
Amortized Cost Basis
Issued by Fannie Mae, Freddie Mac, or Ginnie Mae	$	112,983	$	236,800
Issued by political subdivisions	—		4,253
Other	3,903		508
	$	116,886	$	241,561
Unrealized Loss
Issued by Fannie Mae, Freddie Mac, or Ginnie Mae	$	3,111	$	5,895
Issued by political subdivisions	—		92
Other	53		9
	$	3,164	$	5,996

The Fannie Mae, Freddie Mac, and Ginnie Mae securities are rated AA+ by S&P and Aaa by Moodys.

The amortized cost and estimated fair value of investment securities by maturity at December 31, 2016 are presented in the following table. Securities are classified according to their contractual maturities without consideration of principal amortization, potential prepayments or call options. Accordingly, actual maturities may differ from contractual maturities. Weighted average yields are calculated on the basis of the yield to maturity based on the amortized cost of each security.



	Securities Available for Sale						Securities Held to Maturity
(Dollars in thousands)	Weighted Average Yield		Amortized Cost		Estimated Fair Value		Weighted Average Yield		Amortized Cost		Estimated Fair Value
Within one year or less	2.29	%	$	15,540	$	15,477	2.59	%	$	2,551	$	2,570
One through five years	1.65		283,914		284,150		2.95		9,903		10,082
After five through ten years	2.25		703,768		697,829		3.07		18,181		18,569
Over ten years	2.05		2,483,052		2,448,641		2.81		58,581		58,711
	2.06	%	$	3,486,274	$	3,446,097	2.88	%	$	89,216	$	89,932

The following is a summary of realized gains and losses from the sale of securities classified as available for sale. Gains or losses on securities sold are recorded on the trade date, using the specific identification method.



	Years Ended December 31
(Dollars in thousands)	2016			2015			2014
Realized gains	$	2,949		$	1,834		$	863
Realized losses	(948		)	(259		)	(92		)
	$	2,001		$	1,575		$	771

In addition to the gains above, the Company realized certain gains on calls of securities held to maturity that were not significant to the consolidated financial statements.

Other Equity Securities

The Company accounts for the following securities at amortized cost, which approximates fair value, in “other assets” on the consolidated balance sheets at December 31:



(Dollars in thousands)	2016		2015
Federal Home Loan Bank (FHLB) stock	$	42,326	$	16,265
Federal Reserve Bank (FRB) stock	48,584		48,584
Other investments	2,808		1,159
	$	93,718	$	66,008