The amortized cost, gross unrealized gains and losses, and fair value of investments in fixed income securities classified as available-for-sale at March 31, 2020 and December 31, 2019 are shown in tables 7.1a and 7.1b below.



Details of fixed income securities by category as of March 31, 2020
Table	7.1a
(In thousands)		Amortized Cost		Gross Unrealized Gains		Gross Unrealized (Losses) ⁽¹⁾			Fair Value
U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	197,330	$	2,408	$	(21	)	$	199,717
Obligations of U.S. states and political subdivisions		1,614,562		99,532		(3,258		)	1,710,836
Corporate debt securities		2,508,051		44,386		(41,335		)	2,511,102
Asset backed securities (“ABS”)		210,930		2,031		(6,311		)	206,650
Residential mortgage backed securities (“RMBS”)		259,641		6,032		(758		)	264,915
Commercial mortgage backed securities (“CMBS”)		268,598		3,161		(3,172		)	268,587
Collateralized loan obligations (“CLOs”)		316,270		—		(19,231		)	297,039
Total fixed income securities		$	5,375,382	$	157,550	$	(74,086	)	$	5,458,846



Details of fixed income securities by category as of December 31, 2019
Table	7.1b
(In thousands)		Amortized Cost		Gross Unrealized Gains		Gross Unrealized (Losses) ⁽²⁾			Fair Value
U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	195,176	$	1,237	$	(210	)	$	196,203
Obligations of U.S. states and political subdivisions		1,555,394		99,328		(857		)	1,653,865
Corporate debt securities		2,711,910		76,220		(3,008		)	2,785,122
ABS		227,376		2,466		(178		)	229,664
RMBS		271,384		429		(3,227		)	268,586
CMBS		274,234		5,531		(779		)	278,986
CLOs		327,076		33		(1,643		)	325,466
Total fixed income securities		$	5,562,550	$	185,244	$	(9,902	)	$	5,737,892

We had $14.2 million and $13.9 million of investments at fair value on deposit with various states as of March 31, 2020 and December 31, 2019, respectively, due to regulatory requirements of those state insurance departments.

The amortized cost and fair values of fixed income securities at March 31, 2020, by contractual maturity, are shown in table 7.2 below. Actual maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Because most ABS, RMBS, CMBS, and CLOs provide for periodic payments throughout their lives, they are listed in separate categories.



Fixed income securities maturity schedule
Table	7.2
		March 31, 2020
(In thousands)		Amortized cost		Fair Value
Due in one year or less		$	421,097	$	421,290
Due after one year through five years		1,774,678		1,782,206
Due after five years through ten years		994,134		1,021,561
Due after ten years		1,130,034		1,196,598
		4,319,943		4,421,655

ABS		210,930		206,650
RMBS		259,641		264,915
CMBS		268,598		268,587
CLOs		316,270		297,039
Total as of March 31, 2020		$	5,375,382	$	5,458,846

Proceeds from sales of fixed income securities classified as available-for-sale were $212.8 million and $106.0 million during the three months ended March 31, 2020 and 2019, respectively. During the three months ended March 31, 2020, gross gains and gross losses of $5.1 million and $1.3 million, respectively, were realized on those sales, and we recorded realized losses of $0.3 million related to our intent to sell certain securities. During the three months ended March 31, 2019, gross gains and gross losses of $0.7 million and gross losses of $1.3 million were realized on those sales, and we recorded OTTI losses of $0.1 million.



Details of equity security investments as of March 31, 2020
Table	7.3a
(In thousands)		Cost		Gross Gains		Gross Losses			Fair Value
Equity securities		$	29,559	$	99	$	(766	)	$	28,892



Details of equity security investments as of December 31, 2019
Table	7.3b
(In thousands)		Cost		Gross Gains		Gross Losses			Fair Value
Equity securities		$	17,188	$	154	$	(14	)	$	17,328

For the three months ended March 31, 2020, we recognized $(0.8) million of net losses on equity securities still held as of March 31, 2020. For the three months ended March 31, 2019, we recognized $0.1 million of net gains on equity securities still held as of March 31, 2019.

Other invested assets include an investment in Federal Home Loan Bank ("FHLB") stock that is carried at cost, which due to its nature approximates fair value. Ownership of FHLB stock provides access to a secured lending facility, and our current FHLB Advance amount is secured by eligible collateral whose fair value is maintained at a minimum of 102% of the outstanding principal balance of the FHLB Advance. As of March 31, 2020, that collateral consisted of fixed income securities included in our total investment portfolio, and cash and cash equivalents, with a total fair value of $164.9 million.

Tables 7.4a and 7.4b below summarize, for all available-for-sale investments in an unrealized loss position at March 31, 2020 and December 31, 2019, the aggregate fair value and gross unrealized loss by the length of time those securities have been continuously in an unrealized loss position. The fair value amounts reported in tables 7.4a and 7.4b are estimated using the process described in Note 8 - “Fair Value Measurements” to these consolidated financial statements and in Note 3 - “Significant Accounting Policies” of the notes to the consolidated financial statements in our 2019 Annual Report on Form 10-K.



Unrealized loss aging for securities by type and length of time as of March 31, 2020
Table	7.4a
		Less Than 12 Months					12 Months or Greater					Total
(In thousands)		Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	12,558	$	(21	)	$	—	$	—		$	12,558	$	(21	)
Obligations of U.S. states and political subdivisions		99,354		(3,255		)	2,017		(3		)	101,371		(3,258		)
Corporate debt securities		1,034,108		(41,208		)	907		(127		)	1,035,015		(41,335		)
ABS		64,104		(6,311		)	—		—			64,104		(6,311		)
RMBS		7,664		(60		)	62,645		(698		)	70,309		(758		)
CMBS		133,290		(3,086		)	7,593		(86		)	140,883		(3,172		)
CLOs		186,582		(10,075		)	110,457		(9,156		)	297,039		(19,231		)
Total		$	1,537,660	$	(64,016	)	$	183,619	$	(10,070	)	$	1,721,279	$	(74,086	)



Unrealized loss aging for securities by type and length of time as of December 31, 2019
Table	7.4b
		Less Than 12 Months					12 Months or Greater					Total
(In thousands)		Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	57,301	$	(200	)	$	5,806	$	(10	)	$	63,107	$	(210	)
Obligations of U.S. states and political subdivisions		74,859		(847		)	6,957		(10		)	81,816		(857		)
Corporate debt securities		221,357		(2,847		)	43,505		(161		)	264,862		(3,008		)
ABS		21,542		(118		)	3,851		(60		)	25,393		(178		)
RMBS		105,443		(461		)	110,452		(2,766		)	215,895		(3,227		)
CMBS		62,388		(728		)	11,852		(51		)	74,240		(779		)
CLOs		81,444		(225		)	196,988		(1,418		)	278,432		(1,643		)
Total		$	624,334	$	(5,426	)	$	379,411	$	(4,476	)	$	1,003,745	$	(9,902	)

Based on current facts and circumstances, we believe the unrealized losses as of March 31, 2020 presented in table 7.4a above are not indicative of the ultimate collectability of the current amortized cost of the securities. We believe the gross unrealized losses are primarily attributable to widening credit spreads over risk free rates beyond historic norms, as a result of market uncertainties arising from the COVID-19 pandemic, which includes demand shocks in multiple sectors that originated in the first quarter of 2020.

The unrealized losses in all categories of our investments at December 31, 2019 were primarily caused by changes in interest rates between the time of purchase and December 31, 2019.