Debt Securities Available for Sale and Debt Securities Held to Maturity

The following tables present the adjusted cost and approximate fair value of debt securities available for sale and debt securities held to maturity.



	March 31, 2018
			Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
	(In Thousands)
Debt securities available for sale:
U.S. Treasury and other U.S. government agencies	$	4,908,132	$	2,753	$	116,553	$	4,794,332
Agency mortgage-backed securities	2,666,049		9,961		54,132		2,621,878
Agency collateralized mortgage obligations	4,105,306		4,739		93,756		4,016,289
States and political subdivisions	1,568		85		—		1,653
Total	$	11,681,055	$	17,538	$	264,441	$	11,434,152
Debt securities held to maturity:
Collateralized mortgage obligations:
Agency	$	949,177	$	—	$	14,829	$	934,348
Non-agency	60,491		5,896		2,591		63,796
Asset-backed securities	8,316		1,686		540		9,462
States and political subdivisions	897,084		9,183		7,374		898,893
Other	60,661		1,371		535		61,497
Total	$	1,975,729	$	18,136	$	25,869	$	1,967,996



	December 31, 2017
			Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
	(In Thousands)
Debt securities available for sale:
U.S. Treasury and other U.S. government agencies	$	4,265,296	$	996	$	61,854	$	4,204,438
Agency mortgage-backed securities	2,841,584		14,312		43,096		2,812,800
Agency collateralized mortgage obligations	5,302,531		4,203		106,723		5,200,011
States and political subdivisions	2,278		105		—		2,383
Total	$	12,411,689	$	19,616	$	211,673	$	12,219,632
Debt securities held to maturity:
Non-agency collateralized mortgage obligations	$	64,140	$	5,262	$	1,605	$	67,797
Asset-backed securities	9,308		1,747		628		10,427
States and political subdivisions	911,393		3,951		12,853		902,491
Other	61,252		243		1,667		59,828
Total	$	1,046,093	$	11,203	$	16,753	$	1,040,543

The investments held within the states and political subdivision caption of debt securities held to maturity relate to private placement transactions underwritten as loans by the Company but that meet the definition of a security within ASC Topic 320, Investments – Debt and Equity Securities.

During the three months ended March 31, 2018, the Company transferred approximately $1.0 billion of agency collateralized mortgage backed securities from available for sale to held to maturity.

The following tables disclose the fair value and the gross unrealized losses of the Company’s available for sale debt securities and held to maturity debt securities that were in a loss position at March 31, 2018 and December 31, 2017. This information is aggregated by investment category and the length of time the individual securities have been in an unrealized loss position.



	March 31, 2018
	Securities in a loss position for less than 12 months				Securities in a loss position for 12 months or longer				Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
	(In Thousands)
Debt securities available for sale:
U.S. Treasury and other U.S. government agencies	$	2,842,522	$	68,207	$	1,347,030	$	48,346	$	4,189,552	$	116,553
Agency mortgage-backed securities	439,002		5,363		1,575,272		48,769		2,014,274		54,132
Agency collateralized mortgage obligations	1,091,296		11,567		2,261,506		82,189		3,352,802		93,756
Total	$	4,372,820	$	85,137	$	5,183,808	$	179,304	$	9,556,628	$	264,441

Debt securities held to maturity:
Collateralized mortgage obligations:
Agency	$	—	$	—	$	934,348	$	14,829	$	934,348	$	14,829
Non-agency	2,003		257		23,039		2,334		25,042		2,591
Asset-backed securities	—		—		5,753		540		5,753		540
States and political subdivisions	66,653		605		291,117		6,769		357,770		7,374
Other	—		—		13,389		535		13,389		535
Total	$	68,656	$	862	$	1,267,646	$	25,007	$	1,336,302	$	25,869



	December 31, 2017
	Securities in a loss position for less than 12 months				Securities in a loss position for 12 months or longer				Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
	(In Thousands)
Debt securities available for sale:
U.S. Treasury and other U.S. government agencies	$	2,532,439	$	28,308	$	1,325,975	$	33,546	$	3,858,414	$	61,854
Agency mortgage-backed securities	390,106		2,731		1,666,045		40,365		2,056,151		43,096
Agency collateralized mortgage obligations	1,244,416		6,522		3,297,278		100,201		4,541,694		106,723
Total	$	4,166,961	$	37,561	$	6,289,298	$	174,112	$	10,456,259	$	211,673

Debt securities held to maturity:
Non-agency collateralized mortgage obligations	$	9,776	$	25	$	22,439	$	1,580	$	32,215	$	1,605
Asset-backed securities	—		—		6,243		628		6,243		628
States and political subdivisions	236,207		4,365		341,090		8,488		577,297		12,853
Other	19,048		98		20,736		1,569		39,784		1,667
Total	$	265,031	$	4,488	$	390,508	$	12,265	$	655,539	$	16,753

As indicated in the previous tables, at March 31, 2018, the Company held certain debt securities in unrealized loss positions. The Company does not intend to sell these securities nor is it more-likely-than-not-that it will be required to sell these securities before their anticipated recovery.

The Company regularly evaluates each available for sale and held to maturity debt security in a loss position for OTTI. In its evaluation, the Company considers such factors as the length of time and the extent to which the fair value has been below cost, the financial condition of the issuer, the Company’s intent to hold the security to an expected recovery in market value and whether it is more likely than not that the Company will have to sell the security before its fair value recovers. Activity related to the credit loss component of the OTTI is recognized in earnings. The portion of OTTI related to all other factors is recognized in other comprehensive income.

Management does not believe that any individual unrealized loss in the Company’s debt securities available for sale or held to maturity portfolios, presented in the preceding tables, represents an OTTI at either March 31, 2018 or December 31, 2017, other than those noted below.

The following table discloses activity related to credit losses for debt securities where a portion of the OTTI was recognized in other comprehensive income.



	Three Months Ended March 31,
	2018		2017
	(In Thousands)
Balance at beginning of period	$	22,824	$	22,582
Reductions for securities paid off during the period (realized)	—		—
Additions for the credit component on debt securities in which OTTI was not previously recognized	—		242
Additions for the credit component on debt securities in which OTTI was previously recognized	309		—
Balance at end of period	$	23,133	$	22,824

For the three months ended March 31, 2018 and 2017, there was $309 thousand and $242 thousand, respectively, of OTTI recognized on held to maturity securities. The debt securities primarily impacted by credit impairment are held to maturity non-agency collateralized mortgage obligations.

The contractual maturities of the securities portfolios are presented in the following table.



March 31, 2018	Amortized Cost		Fair Value
	(In Thousands)
Debt securities available for sale:
Maturing within one year	$	250,930	$	250,048
Maturing after one but within five years	2,338,348		2,275,290
Maturing after five but within ten years	1,492,547		1,473,277
Maturing after ten years	827,875		797,370
	4,909,700		4,795,985
Mortgage-backed securities and collateralized mortgage obligations	6,771,355		6,638,167
Total	$	11,681,055	$	11,434,152

Debt securities held to maturity:
Maturing within one year	$	107,667	$	107,742
Maturing after one but within five years	182,436		183,167
Maturing after five but within ten years	206,061		206,733
Maturing after ten years	469,897		472,210
	966,061		969,852
Collateralized mortgage obligations	1,009,668		998,144
Total	$	1,975,729	$	1,967,996