The following table summarizes the amortized cost and estimated fair value of securities available for sale and securities held to maturity as of March 31, 2020 and December 31, 2019, excluding accrued interest of $13.3 million and $15.1 million, respectively, which is included in other assets in the unaudited consolidated balance sheets, and the corresponding amounts of gross unrealized gains and losses recognized in accumulated other comprehensive income (loss) and gross unrecognized gains and losses:



	March 31, 2020
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Securities available for sale:
U.S. Government-sponsored enterprise obligations	$	39,944	$	425	$	—		$	40,369
Obligations of state and political subdivisions	158,578		6,984		—			165,562
Mortgage-backed securities:
Residential agency	2,797,087		82,191		(70		)	2,879,208
Commercial agency	681,145		32,078		(13		)	713,210
Other securities	113,621		3,230		(240		)	116,611
Total securities available for sale	$	3,790,375	$	124,908	$	(323	)	$	3,914,960

	Amortized Cost		Gross Unrecognized Gains		Gross Unrecognized Losses			Estimated Fair Value
Securities held to maturity:
Obligations of state and political subdivisions	$	162,330	$	8,233	$	—		$	170,563
Mortgage-backed securities:
Residential agency	15,630		210		(7		)	15,833
Total securities held to maturity	$	177,960	$	8,443	$	(7	)	$	186,396



	December 31, 2019
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Securities available for sale:
U.S. Government-sponsored enterprise obligations	$	39,916	$	281	$	—		$	40,197
Obligations of state and political subdivisions	160,873		7,607		—			168,480
Mortgage-backed securities:
Residential agency	2,876,069		27,423		(3,836		)	2,899,656
Commercial agency	704,661		17,202		(404		)	721,459
Other securities	101,022		2,779		(233		)	103,568
Total securities available for sale	$	3,882,541	$	55,292	$	(4,473	)	$	3,933,360

	Amortized Cost		Gross Unrecognized Gains		Gross Unrecognized Losses			Estimated Fair Value
Securities held to maturity:
Obligations of state and political subdivisions	$	166,386	$	7,147	$	—		$	173,533
Mortgage-backed securities:
Residential agency	16,575		30		(239		)	16,366
Total securities held to maturity	$	182,961	$	7,177	$	(239	)	$	189,899



	March 31, 2020
	Less Than Twelve Months					Twelve Months or More					Total
(in thousands)	Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value
Securities available for sale:
Mortgage-backed securities:
Residential agency	$	(70	)	$	8,684	$	—		$	—	$	(70	)	$	8,684
Commercial agency	(13		)	5,039		—			—		(13		)	5,039
Other securities	(152		)	19,848		(88		)	4,168		(240		)	24,016
Total securities available for sale	$	(235	)	$	33,571	$	(88	)	$	4,168	$	(323	)	$	37,739

	Less Than Twelve Months					Twelve Months or More					Total
	Gross Unrecognized Losses			Estimated Fair Value		Gross Unrecognized Losses			Estimated Fair Value		Gross Unrecognized Losses			Estimated Fair Value
Securities held to maturity:
Mortgage-backed securities:
Residential agency	$	—		$	46	$	(7	)	$	1,973	$	(7	)	$	2,019
Total securities held to maturity	$	—		$	46	$	(7	)	$	1,973	$	(7	)	$	2,019



	December 31, 2019
	Less Than Twelve Months					Twelve Months or More					Total
(in thousands)	Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value
Securities available for sale:
Obligations of state and political subdivisions	$	—		$	590	$	—		$	—	$	—		$	590
Mortgage-backed securities:
Residential agency	(1,893		)	441,332		(1,943		)	268,383		(3,836		)	709,715
Commercial agency	(252		)	56,728		(152		)	10,301		(404		)	67,029
Other securities	(133		)	13,241		(100		)	4,492		(233		)	17,733
Total securities available for sale	$	(2,278	)	$	511,891	$	(2,195	)	$	283,176	$	(4,473	)	$	795,067


	Less Than Twelve Months					Twelve Months or More					Total
	Gross Unrecognized Losses			Estimated Fair Value		Gross Unrecognized Losses			Estimated Fair Value		Gross Unrecognized Losses			Estimated Fair Value
Securities held to maturity:
Mortgage-backed securities:
Residential agency	$	(52	)	$	6,308	$	(187	)	$	9,074	$	(239	)	$	15,382
Total securities held to maturity	$	(52	)	$	6,308	$	(187	)	$	9,074	$	(239	)	$	15,382

The Company held certain investment securities where amortized cost exceeded fair value, resulting in unrealized loss positions, as shown in the tables above. The Company evaluates its investment securities portfolio for impairment on a quarterly basis.

For HTM securities, the Company maintains an allowance for expected credit losses appropriate to absorb estimated lifetime credit losses. HTM securities where there is a risk of credit loss are segmented by credit rating and duration and an allowance for expected credit losses is calculated based on external historical loss data, taking into consideration management's forecast of future economic conditions. The Company has assessed the risk of credit loss and has determined the allowance for expected credit losses for HTM securities to be immaterial as of March 31, 2020.

For AFS securities, declines in the fair value of individual securities below their amortized cost basis are reviewed to determine if the decline is due to credit-related factors. As of March 31, 2020, unrealized losses on AFS securities have not been recognized into income because the issuers are of high credit quality, management does not intend to sell and it is likely that management will not be required to sell the securities prior to their anticipated recovery, and the decline in fair value is largely due to changes in interest rates and other market conditions. Therefore, no allowance for expected credit losses has been recorded for AFS securities as of March 31, 2020 and the unrealized losses are recognized in other comprehensive income.

Prior to January 1, 2020, management evaluated HTM and AFS securities for other-than-temporary impairment. Impairment was considered to be other-than-temporary if the Company (1) intended to sell the security, (2) more likely than not would be required to sell the security before recovering its cost, or (3) did not expect to recover the security's entire amortized cost basis. As of December 31, 2019, the Company did not intend to sell any of these securities, did not expect to be required to sell these securities, and expected to recover the entire amortized cost of all these securities. 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, 2019.

At March 31, 2020, 13 debt securities had unrealized losses of 0.82% of the securities’ amortized cost basis. At December 31, 2019, 123 debt securities had unrealized losses of 0.58% of the securities’ amortized cost basis. Additional information on securities that were in a continuous loss position for over twelve months at March 31, 2020 and December 31, 2019 is presented in the following table.



(in thousands)	March 31, 2020		December 31, 2019
Number of securities
Mortgage-backed securities:
Residential agency	2		59
Commercial agency	—		6
Other securities	4		4
	6		69
Amortized Cost Basis
Mortgage-backed securities:
Residential agency	$	1,980	$	279,587
Commercial agency	—		10,453
Other securities	4,256		4,591
	$	6,236	$	294,631
Unrealized Loss
Mortgage-backed securities:
Residential agency	$	7	$	2,130
Commercial agency	—		152
Other securities	88		100
	$	95	$	2,382

A substantial portion of the Company's HTM securities portfolio consists of obligations of state and political subdivisions. The Company monitors the credit quality of these securities through the use of credit ratings on a quarterly basis. The following table summarizes the amortized cost of HTM obligations of state and political subdivisions at March 31, 2020, aggregated by credit quality indicator:

At March 31, 2020, the Company also held HTM residential agency mortgage-backed securities with an amortized cost of $15.6 million. This portfolio includes Frannie Mae and Freddie Mac securities which are considered to be government sponsored enterprises (GSEs). While securities issued by GSEs do carry credit risk, the company considered the risks and determined that the risk of credit loss for these securities was zero.

The amortized cost and estimated fair value of investment securities by maturity at March 31, 2020 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
(in thousands)	Weighted Average Yield		Amortized Cost		Estimated Fair Value		Weighted Average Yield		Amortized Cost		Estimated Fair Value
Within one year or less	2.62	%	$	41,572	$	41,999	3.00	%	$	245	$	245
One through five years	2.60		180,356		187,480		2.59		5,329		5,380
After five through ten years	2.68		641,404		671,014		2.37		56,038		58,524
Over ten years	2.59		2,927,043		3,014,467		2.56		116,348		122,247
	2.61	%	$	3,790,375	$	3,914,960	2.50	%	$	177,960	$	186,396

Gains or losses on securities sold are recorded on the trade date, using the specific identification method. For the three months ended March 31, 2020 and 2019, the Company did not have any realized gains or losses from the sale of securities classified as available for sale. The Company did not realize any gains on calls of securities held to maturity for the three months ended March 31, 2020 and 2019.

The Company accounts for the following securities at cost less impairment plus or minus any observable price changes, which approximates fair value, with the exception of CRA and Community Development Investment Funds, which are recorded at fair value. Other equity securities, which are presented in other assets on the consolidated balance sheets, were as follows:



(in thousands)	March 31, 2020		December 31, 2019
Federal Home Loan Bank stock	$	70,914	$	70,386
Federal Reserve Bank stock	85,630		85,630
CRA and Community Development Investment Funds	1,988		1,948
Other investments	22,098		21,118
	$	180,630	$	179,082