INVESTMENT SECURITIES

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



	September 30, 2017
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Securities available for sale:
U.S. Government-sponsored enterprise obligations	$	60,940	$	99	$	(171	)	$	60,868
Obligations of state and political subdivisions	273,938		5,226		(1,516		)	277,648
Mortgage-backed securities	4,300,673		7,448		(29,968		)	4,278,153
Other securities	119,553		553		(436		)	119,670
Total securities available for sale	$	4,755,104	$	13,326	$	(32,091	)	$	4,736,339
Securities held to maturity:
Obligations of state and political subdivisions	$	153,775	$	1,413	$	(483	)	$	154,705
Mortgage-backed securities	22,131		47		(568		)	21,610
Total securities held to maturity	$	175,906	$	1,460	$	(1,051	)	$	176,315



	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

Securities with carrying values of $1.9 billion and $1.5 billion were pledged to secure public deposits and other borrowings at September 30, 2017 and December 31, 2016, 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:



	September 30, 2017
	Less Than Twelve Months					Twelve Months or More					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	$	(171	)	$	54,825	$	—		$	—	$	(171	)	$	54,825
Obligations of state and political subdivisions	(204		)	29,563		(1,312		)	68,827		(1,516		)	98,390
Mortgage-backed securities	(18,703		)	2,416,882		(11,265		)	474,232		(29,968		)	2,891,114
Other Securities	(420		)	67,683		(16		)	1,324		(436		)	69,007
Total securities available for sale	$	(19,498	)	$	2,568,953	$	(12,593	)	$	544,383	$	(32,091	)	$	3,113,336

Securities held to maturity:
Obligations of state and political subdivisions	$	(456	)	$	85,456	$	(27	)	$	3,031	$	(483	)	$	88,487
Mortgage-backed securities	(20		)	2,096		(548		)	19,117		(568		)	21,213
Total securities held to maturity	$	(476	)	$	87,552	$	(575	)	$	22,148	$	(1,051	)	$	109,700



	December 31, 2016
	Less Than Twelve Months					Twelve Months or More					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 subdivisions	(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 subdivisions	$	(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

The Company assessed the nature of the unrealized losses in its portfolio as of September 30, 2017 and December 31, 2016 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 September 30, 2017 or December 31, 2016.

At September 30, 2017, 439 debt securities had unrealized losses of 1.02% of the securities’ amortized cost basis. At December 31, 2016, 397 debt securities had unrealized losses of 1.79% 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 September 30, 2017 and December 31, 2016 is presented in the following table.



(Dollars in thousands)	September 30, 2017		December 31, 2016
Number of securities:
Mortgage-backed securities	91		28
Obligations of state and political subdivisions	28		—
Other	2		3
	121		31
Amortized Cost Basis:
Mortgage-backed securities	$	505,161	$	112,983
Obligations of state and political subdivisions	73,197		—
Other	1,341		3,903
	$	579,699	$	116,886
Unrealized Loss:
Mortgage-backed securities	$	11,812	$	3,111
Obligations of state and political subdivisions	1,339		—
Other	17		53
	$	13,168	$	3,164

The securities noted above carry a rating of AA+/AA- by S&P and Aaa/Aa3 by Moody's.

The amortized cost and estimated fair value of investment securities by maturity at September 30, 2017 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	0.65	%	$	38,171	$	38,071	2.86	%	$	1,629	$	1,642
One through five years	2.02		133,177		133,407		3.01		8,736		8,838
After five through ten years	2.38		840,457		842,821		2.80		35,075		35,733
Over ten years	2.28		3,743,299		3,722,040		2.59		130,466		130,102
	2.27	%	$	4,755,104	$	4,736,339	2.66	%	$	175,906	$	176,315

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.



	Three Months Ended September 30,					Nine Months Ended September 30,
(Dollars in thousands)	2017			2016		2017			2016
Realized gains	$	667		$	12	$	909		$	2,947
Realized losses	(909		)	—		(1,092		)	(950		)
	$	(242	)	$	12	$	(183	)	$	1,997

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:



(Dollars in thousands)	September 30, 2017		December 31, 2016
Federal Home Loan Bank (FHLB) stock	$	93,672	$	42,326
Federal Reserve Bank (FRB) stock	64,728		48,584
Other investments	3,008		2,808
	$	161,408	$	93,718