Investment Securities (Tables)

12 Months Ended

Dec. 31, 2018

Investment Securities

Schedule of amortized cost and fair value of securities

	2018								2017
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
(dollars in thousands)	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury securities	$	389,470	$	—	$	—	$	389,470	$	404,376	$	—	$	(12,121)	$	392,255
Government-sponsored enterprises debt securities		248,372		—		(6,778)		241,594		249,712		—		(7,111)		242,601
Government agency mortgage-backed securities		426,710		—		(15,174)		411,536		356,858		—		(5,468)		351,390
Government-sponsored enterprises mortgage-backed securities		156,056		85		(5,294)		150,847		178,702		169		(4,130)		174,741
Collateralized mortgage obligations:
Government agency		2,779,620		—		(97,171)		2,682,449		3,367,173		47		(76,746)		3,290,474
Government-sponsored enterprises		620,337		—		(17,745)		602,592		779,911		25		(17,218)		762,718
Debt securities issued by states and political subdivisions		19,854		—		—		19,854		20,543		—		(64)		20,479
Total available-for-sale securities	$	4,640,419	$	85	$	(142,162)	$	4,498,342	$	5,357,275	$	241	$	(122,858)	$	5,234,658

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

	December 31, 2018
	Amortized		Fair
(dollars in thousands)	Cost		Value
Due after one year through five years	$	523,117	$	521,453
Due after five years through ten years		114,725		109,611
Due after ten years		19,854		19,854
		657,696		650,918
Government agency mortgage-backed securities		426,710		411,536
Government-sponsored enterprises mortgage-backed securities		156,056		150,847
Collateralized mortgage obligations:
Government agency		2,779,620		2,682,449
Government-sponsored enterprises		620,337		602,592
Total mortgage-backed securities and collateralized mortgage obligations		3,982,723		3,847,424
Total available-for-sale securities	$	4,640,419	$	4,498,342

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

	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
Government agency mortgage-backed securities		—		—		(15,174)		373,891		(15,174)		373,891
Government-sponsored enterprises mortgage-backed securities		(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

	Time in Continuous Loss as of December 31, 2017
	Less Than 12 Months				12 Months or More				Total
	Unrealized				Unrealized				Unrealized
(dollars in thousands)	Losses		Fair Value		Losses		Fair Value		Losses		Fair Value
U.S. Treasury securities	$	(994)	$	48,182	$	(11,127)	$	344,073	$	(12,121)	$	392,255
Government-sponsored enterprises debt securities		(642)		59,358		(6,469)		183,243		(7,111)		242,601
Government agency mortgage-backed securities		(976)		200,963		(4,492)		150,427		(5,468)		351,390
Government-sponsored enterprises mortgage-backed securities		(1)		63		(4,129)		168,342		(4,130)		168,405
Collateralized mortgage obligations:
Government agency		(23,236)		1,473,170		(53,510)		1,803,338		(76,746)		3,276,508
Government-sponsored enterprises		(3,203)		327,435		(14,015)		403,321		(17,218)		730,756
Debt securities issued by states and political subdivisions		(64)		10,641		—		—		(64)		10,641
Total available-for-sale securities with unrealized losses	$	(29,116)	$	2,119,812	$	(93,742)	$	3,052,744	$	(122,858)	$	5,172,556

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)
Government agency mortgage-backed securities		(146)
Government-sponsored enterprises mortgage-backed securities		(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)