Investment Securities (Tables)

12 Months Ended

Dec. 31, 2019

Investment Securities

Schedule of amortized cost and fair value of securities

	2019								2018
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
(dollars in thousands)	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury securities	$	29,832	$	56	$	—	$	29,888	$	389,470	$	—	$	—	$	389,470
Government-sponsored enterprises debt securities		101,697		19		(277)		101,439		248,372		—		(6,778)		241,594
Mortgage-backed securities:
Residential - Government agency		290,131		2,224		(1,146)		291,209		426,710		—		(15,174)		411,536
Residential - Government-sponsored enterprises		395,039		6,126		(1,673)		399,492		156,056		85		(5,294)		150,847
Commercial - Government-sponsored enterprises		101,798		555		(634)		101,719		—		—		—		—
Collateralized mortgage obligations:
Government agency		2,390,143		7,483		(16,348)		2,381,278		2,779,620		—		(97,171)		2,682,449
Government-sponsored enterprises		772,023		2,505		(3,909)		770,619		620,337		—		(17,745)		602,592
Debt securities issued by states and political subdivisions		—		—		—		—		19,854		—		—		19,854
Total available-for-sale securities	$	4,080,663	$	18,968	$	(23,987)	$	4,075,644	$	4,640,419	$	85	$	(142,162)	$	4,498,342

Schedule of amortized cost and fair value of debt securities by contractual maturity

	December 31, 2019
	Amortized		Fair
(dollars in thousands)	Cost		Value
Due in one year or less	$	29,832	$	29,888
Due after one year through five years		101,697		101,439
Due after five years through ten years		—		—
Due after ten years		—		—
		131,529		131,327
Mortgage-backed securities:
Residential - Government agency		290,131		291,209
Residential - Government-sponsored enterprises		395,039		399,492
Commercial - Government-sponsored enterprises		101,798		101,719
Total mortgage-backed securities		786,968		792,420
Collateralized mortgage obligations:
Government agency		2,390,143		2,381,278
Government-sponsored enterprises		772,023		770,619
Total collateralized mortgage obligations		3,162,166		3,151,897
Total available-for-sale securities	$	4,080,663	$	4,075,644

Schedule of gross unrealized losses and fair values of securities in a continuous loss position

	Time in Continuous Loss as of December 31, 2019
	Less Than 12 Months				12 Months or More				Total
	Unrealized				Unrealized				Unrealized
(dollars in thousands)	Losses		Fair Value		Losses		Fair Value		Losses		Fair Value
Government-sponsored enterprises debt securities	$	(277)	$	49,716	$	—	$	—	$	(277)	$	49,716
Mortgage-backed securities:
Residential - Government agency		—		—		(1,146)		109,614		(1,146)		109,614
Residential - Government-sponsored enterprises		(115)		76,481		(1,558)		109,025		(1,673)		185,506
Commercial - Government-sponsored enterprises		(634)		38,062		—		—		(634)		38,062
Collateralized mortgage obligations:
Government agency		(8,049)		969,762		(8,299)		565,764		(16,348)		1,535,526
Government-sponsored enterprises		(583)		180,785		(3,326)		209,752		(3,909)		390,537
Total available-for-sale securities with unrealized losses	$	(9,658)	$	1,314,806	$	(14,329)	$	994,155	$	(23,987)	$	2,308,961

	Time in Continuous Loss as of December 31, 2018
	Less Than 12 Months				12 Months or More				Total
	Unrealized				Unrealized				Unrealized
(dollars in thousands)	Losses		Fair Value		Losses		Fair Value		Losses		Fair Value
Government-sponsored enterprises debt securities	$	—	$	—	$	(6,778)	$	157,939	$	(6,778)	$	157,939
Mortgage-backed securities:
Residential - Government agency		—		—		(15,174)		373,891		(15,174)		373,891
Residential - Government-sponsored enterprises		(1)		172		(5,293)		125,869		(5,294)		126,041
Collateralized mortgage obligations:
Government agency		—		—		(97,171)		2,475,532		(97,171)		2,475,532
Government-sponsored enterprises		—		—		(17,745)		486,175		(17,745)		486,175
Total available-for-sale securities with unrealized losses	$	(1)	$	172	$	(142,161)	$	3,619,406	$	(142,162)	$	3,619,578

Schedule of OTTI write-downs included in earnings

	Year Ended
(dollars in thousands)	December 31, 2018
U.S. Treasury securities	$	(13,634)
Government-sponsored enterprises debt securities		(1,344)
Mortgage-backed securities:
Residential - Government agency		(146)
Residential - Government-sponsored enterprises		(763)
Collateralized mortgage obligations:
Government agency		(5,064)
Government-sponsored enterprises		(2,711)
Debt securities issued by states and political subdivisions		(423)
Total OTTI write-downs included in earnings	$	(24,085)