The fair value and net unrealized gain (loss) included in trading securities are as follows (in thousands):


	June 30, 2020						December 31, 2019
	Fair Value		Net Unrealized Gain (Loss)		Fair Value		Net Unrealized Gain (Loss)
U.S. government agency debentures	$	4,237	$	19	$	44,264	$	6
Residential agency mortgage-backed securities	1,146,454		3,589		1,504,651		2,293
Municipal and other tax-exempt securities	22,710		116		26,196		60
Asset-backed securities	5		—		14,084		(21)
Other debt securities	22,699		127		34,726		21
Total trading securities	$	1,196,105	$	3,851	$	1,623,921	$	2,359


	June 30, 2020
	Amortized		Fair		Gross Unrealized
	Cost		Value		Gain		Loss
Municipal and other tax-exempt	$	84,239	$	88,623	$	4,384	$	—
Residential agency mortgage-backed securities	9,812		10,734		922		—
Other debt securities	175,565		199,769		24,235		(31)
Total investment securities	269,616		299,126		29,541		(31)
Allowance for credit losses¹	(1,628)
Investment securities, net of allowance	267,988		299,126		29,541		(31)

¹ Effective with the adoption of FASB ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326) on January 1, 2020.


	December 31, 2019
	Amortized		Fair		Gross Unrealized
	Cost		Value		Gain		Loss
Municipal and other tax-exempt	$	93,653	$	96,897	$	3,250	$	(6)
Residential agency mortgage-backed securities	10,676		11,164		488		—
Other debt securities	189,089		206,341		17,547		(295)
Total investment securities	$	293,418	$	314,402	$	21,285	$	(301)

The amortized cost and fair values of investment securities at June 30, 2020, by contractual maturity, are as shown in the following table (dollars in thousands):


	Less than One Year		One to Five Years		Six to Ten Years		Over Ten Years		Total		Weighted Average Maturity¹
Fixed maturity debt securities:
Amortized cost	$	39,734	$	87,863	$	122,309	$	9,898	$	259,804	4.95
Fair value	40,151		96,615		141,378		10,248		288,392
Residential mortgage-backed securities:
Amortized cost									$	9,812	2
Fair value									10,734
Total investment securities:
Amortized cost									$	269,616
Fair value									299,126

¹Expected maturities may differ from contractual maturities, because borrowers may have the right to call or prepay obligations with or without penalty.

²The average expected lives of residential mortgage-backed securities were 4.6 years based upon current prepayment assumptions.


	June 30, 2020
	Number of Securities	Less Than 12 Months									12 Months or Longer									Total
				Fair Value			Unrealized Loss			Fair Value			Unrealized Loss			Fair Value			Unrealized Loss
Investment:


Other debt securities	4	—			—			2,142			31			2,142			31
Total investment securities	4	$	—		$	—		$	2,142		$	31		$	2,142		$	31


	December 31, 2019
	Number of Securities	Less Than 12 Months									12 Months or Longer									Total
				Fair Value			Unrealized Loss			Fair Value			Unrealized Loss			Fair Value			Unrealized Loss
Investment:
Municipal and other tax-exempt	4	$	1,001		$	1		$	1,706		$	5		$	2,707		$	6

Other debt securities	13	275			1			8,041			294			8,316			295
Total investment securities	17	$	1,276		$	2		$	9,747		$	299		$	11,023		$	301


	June 30, 2020
	Amortized		Fair		Gross Unrealized
	Cost		Value		Gain		Loss
U.S. Treasury	$	900	$	912	$	12	$	—
Municipal and other tax-exempt	29,670		31,240		1,570		—
Mortgage-backed securities:
Residential agency	8,789,466		9,147,238		360,056		(2,284)
Residential non-agency	21,941		35,250		13,318		(9)
Commercial agency	3,146,108		3,260,807		116,042		(1,343)
Other debt securities	500		472		—		(28)
Total available for sale securities	$	11,988,585	$	12,475,919	$	490,998	$	(3,664)


	December 31, 2019
	Amortized		Fair		Gross Unrealized
	Cost		Value		Gain		Loss
U.S. Treasury	$	1,598	$	1,600	$	2	$	—
Municipal and other tax-exempt	1,789		1,861		72		—
Mortgage-backed securities:
Residential agency	7,956,297		8,046,096		104,912		(15,113)
Residential non-agency	25,968		41,609		15,641		—
Commercial agency	3,145,342		3,178,005		37,808		(5,145)
Other debt securities	500		472		—		(28)
Total available for sale securities	$	11,131,494	$	11,269,643	$	158,435	$	(20,286)

The amortized cost and fair values of available for sale securities at June 30, 2020, by contractual maturity, are as shown in the following table (dollars in thousands):


	Less than One Year		One to Five Years		Six to Ten Years		Over Ten Years		Total		Weighted Average Maturity¹
Fixed maturity debt securities:
Amortized cost	$	34,044	$	1,321,471	$	1,241,310	$	580,353	$	3,177,178	8.03
Fair value	34,144		1,375,128		1,280,251		603,908		3,293,431
Residential mortgage-backed securities:
Amortized cost									$	8,811,407	2
Fair value									9,182,488
Total available-for-sale securities:
Amortized cost									$	11,988,585
Fair value									12,475,919

¹Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without penalty.

²The average expected lives of residential mortgage-backed securities were 3.1 years based upon current prepayment assumptions.


	Three Months Ended June 30,						Six Months Ended June 30,
	2020		2019		2020		2019
Proceeds	$	179,051	$	122,098	$	205,945	$	367,357
Gross realized gains	5,580		1,029		5,583		6,327
Gross realized losses	—		—		—		(5,222)
Related federal and state income tax expense (benefit)	1,421		262		1,422		281

The fair value of debt securities pledged as collateral for repurchase agreements, public trust funds on deposit and for other purposes, as required by law was $12.3 billion at June 30, 2020 and $10.1 billion at December 31, 2019. The secured parties do not have the right to sell or repledge these securities.


	June 30, 2020
	Number of Securities	Less Than 12 Months									12 Months or Longer									Total
				Fair Value			Unrealized Loss			Fair Value			Unrealized Loss			Fair Value			Unrealized Loss
Available for sale:


Mortgage-backed securities:
Residential agency	36	492,864			1,375			173,997			909			666,861			2,284
Residential non-agency	1	1,695			9			—			—			1,695			9
Commercial agency	22	271,735			902			160,806			441			432,541			1,343
Other debt securities	1	—			—			472			28			472			28
Total available for sale securities	60	$	766,294		$	2,286		$	335,275		$	1,378		$	1,101,569		$	3,664


	December 31, 2019
	Number of Securities	Less Than 12 Months									12 Months or Longer									Total
				Fair Value			Unrealized Loss			Fair Value			Unrealized Loss			Fair Value			Unrealized Loss
Available for sale:


Mortgage-backed securities:
Residential agency	133	$	1,352,597		$	6,690		$	686,002		$	8,423		$	2,038,599		$	15,113

Commercial agency	69	830,047			4,238			210,877			907			1,040,924			5,145
Other debt securities	1	—			—			472			28			472			28
Total available for sale securities	203	$	2,182,644		$	10,928		$	897,351		$	9,358		$	3,079,995		$	20,286

Based on evaluations of impaired securities as of June 30, 2020, the Company does not intend to sell any impaired available for sale debt securities before fair value recovers to the current amortized cost and it is more-likely-than-not that the Company will not be required to sell impaired securities before fair value recovers, which may be maturity.

Fair value option securities represent securities which the Company has elected to carry at fair value and are separately identified on the Consolidated Balance Sheets. Changes in the fair value are recognized in earnings as they occur. Certain securities are held as an economic hedge of the mortgage servicing rights.

The fair value and net unrealized gain (loss) included in fair value option securities is as follows (in thousands):


	June 30, 2020						December 31, 2019
	Fair Value		Net Unrealized Gain (Loss)		Fair Value		Net Unrealized Gain (Loss)
U.S. Treasury	$	92,742	$	307	$	9,917	$	(48)
Residential agency mortgage-backed securities	629,915		16,549		1,088,660		14,109

Total	$	722,657	$	16,856	$	1,098,577	$	14,061