Investment Securities (Tables)

9 Months Ended

Sep. 30, 2018

Investment Securities

Schedule of amortized cost and fair value of securities

	September 30, 2018								December 31, 2017
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
(dollars in thousands)	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury securities	$	403,425	$	—	$	(19,535)	$	383,890	$	404,376	$	—	$	(12,121)	$	392,255
Government-sponsored enterprises debt securities		249,716		—		(12,499)		237,217		249,712		—		(7,111)		242,601
Government agency mortgage-backed securities		439,773		—		(20,480)		419,293		356,858		—		(5,468)		351,390
Government-sponsored enterprises mortgage-backed securities		161,975		93		(7,935)		154,133		178,702		169		(4,130)		174,741
Collateralized mortgage obligations:
Government agency		2,906,962		—		(152,996)		2,753,966		3,367,173		47		(76,746)		3,290,474
Government-sponsored enterprises		657,793		—		(30,554)		627,239		779,911		25		(17,218)		762,718
Debt securities issued by states and political subdivisions		20,344		—		(781)		19,563		20,543		—		(64)		20,479
Total available-for-sale securities	$	4,839,988	$	93	$	(244,780)	$	4,595,301	$	5,357,275	$	241	$	(122,858)	$	5,234,658

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

	September 30, 2018
	Amortized		Fair
(dollars in thousands)	Cost		Value
Due after one year through five years	$	503,416	$	479,725
Due after five years through ten years		149,725		141,382
Due after ten years		20,344		19,563
		673,485		640,670
Government agency mortgage-backed securities		439,773		419,293
Government-sponsored enterprises mortgage-backed securities		161,975		154,133
Collateralized mortgage obligations:
Government agency		2,906,962		2,753,966
Government-sponsored enterprises		657,793		627,239
Total mortgage-backed securities and collateralized mortgage obligations		4,166,503		3,954,631
Total available-for-sale securities	$	4,839,988	$	4,595,301

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

	Time in Continuous Loss as of September 30, 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
U.S. Treasury securities	$	—	$	—	$	(19,535)	$	383,890	$	(19,535)	$	383,890
Government-sponsored enterprises debt securities		(967)		34,033		(11,532)		203,184		(12,499)		237,217
Government agency mortgage-backed securities		(11,097)		291,901		(9,383)		127,392		(20,480)		419,293
Government-sponsored enterprises mortgage-backed securities		(1)		181		(7,934)		148,966		(7,935)		149,147
Collateralized mortgage obligations:
Government agency		(1,166)		44,805		(151,830)		2,709,161		(152,996)		2,753,966
Government-sponsored enterprises		(6,167)		182,303		(24,387)		444,936		(30,554)		627,239
Debt securities issued by states and political subdivisions		(368)		9,402		(413)		10,161		(781)		19,563
Total available-for-sale securities with unrealized losses	$	(19,766)	$	562,625	$	(225,014)	$	4,027,690	$	(244,780)	$	4,590,315

	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