INVESTMENT SECURITIES (Tables)

12 Months Ended

Dec. 31, 2017

INVESTMENT SECURITIES [Abstract]

Amortized Cost and Estimated Fair Value of Investment Securities

The amortized cost and estimated fair value of investment securities as of December 31 are as follows:

	2017								2016
(000's omitted)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-Sale Portfolio:
U.S. Treasury and agency securities	$	2,043,023	$	15,886	$	4,838	$	2,054,071	$	1,876,358	$	28,522	$	2,118	$	1,902,762
Obligations of state and political subdivisions		514,949		14,064		57		528,956		582,655		13,389		1,054		594,990
Government agency mortgage-backed securities		358,180		3,121		3,763		357,538		232,657		5,040		2,467		235,230
Corporate debt securities		2,648		0		25		2,623		5,716		2		31		5,687
Government agency collateralized mortgage obligations		88,097		155		878		87,374		9,225		310		0		9,535
Marketable equity securities		251		275		0		526		252		200		0		452
Total available-for-sale portfolio	$	3,007,148	$	33,501	$	9,561	$	3,031,088	$	2,706,863	$	47,463	$	5,670	$	2,748,656
Other Securities:
Federal Home Loan Bank common stock	$	9,896					$	9,896	$	12,191					$	12,191
Federal Reserve Bank common stock		30,690						30,690		19,781						19,781
Certificates of deposit		3,865						3,865		0						0
Other equity securities		5,840						5,840		3,764						3,764
Total other securities	$	50,291					$	50,291	$	35,736					$	35,736

Summary of Investment Securities That Have Been in a Continuous Unrealized Loss Position for Less Than or Greater Than Twelve Months

A summary of investment securities that have been in a continuous unrealized loss position for less than or greater than twelve months is as follows:

As of December 31, 2017

		Less than 12 Months					12 Months or Longer					Total
(000's omitted)	#	Fair Value		Gross Unrealized Losses		#	Fair Value		Gross Unrealized Losses		#	Fair Value		Gross Unrealized Losses
Available-for-Sale Portfolio:
U.S. Treasury and agency securities	44	$	699,709	$	4,838	0	$	0	$	0	44	$	699,709	$	4,838
Obligations of state and political subdivisions	45		23,432		57	0		0		0	45		23,432		57
Government agency mortgage-backed securities	120		185,716		1,433	55		75,712		2,330	175		261,428		3,763
Corporate debt securities	1		2,623		25	0		0		0	1		2,623		25
Government agency collateralized mortgage obligations	39		80,041		878	1		1		0	40		80,042		878
Total available-for-sale investment portfolio	249	$	991,521	$	7,231	56	$	75,713	$	2,330	305	$	1,067,234	$	9,561

As of December 31, 2016

		Less than 12 Months					12 Months or Longer					Total
(000's omitted)	#	Fair Value		Gross Unrealized Losses		#	Fair Value		Gross Unrealized Losses		#	Fair Value		Gross Unrealized Losses
Available-for-Sale Portfolio:
U.S. Treasury and agency securities	13	$	449,242	$	2,118	0	$	0	$	0	13	$	449,242	$	2,118
Obligations of state and political subdivisions	197		102,106		1,054	0		0		0	197		102,106		1,054
Government agency mortgage-backed securities	57		83,862		1,637	15		21,788		830	72		105,650		2,467
Corporate debt securities	1		2,677		31	0		0		0	1		2,677		31
Government agency collateralized mortgage obligations	0		0		0	2		2		0	2		2		0
Total available-for-sale investment portfolio	268	$	637,887	$	4,840	17	$	21,790	$	830	285	$	659,677	$	5,670

Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity

The amortized cost and estimated fair value of debt securities at December 31, 2017, by contractual maturity, are shown below. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.  Securities not due at a single maturity date are shown separately.

	Available-for-Sale
(000's omitted)	Amortized Cost		Fair Value
Due in one year or less	$	45,966	$	46,042
Due after one through five years		1,565,423		1,572,634
Due after five years through ten years		758,742		769,828
Due after ten years		190,489		197,146
Subtotal		2,560,620		2,585,650
Government agency mortgage-backed securities		358,180		357,538
Government agency collateralized mortgage obligations		88,097		87,374
Total	$	3,006,897	$	3,030,562