Investment Securities (Tables)

3 Months Ended

Mar. 31, 2018

Investment Securities

Schedule of amortized cost and fair value of securities

	March 31, 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	$	404,062	$	—	$	(16,415)	$	387,647	$	404,376	$	—	$	(12,121)	$	392,255
Government-sponsored enterprises debt securities		249,714		—		(10,059)		239,655		249,712		—		(7,111)		242,601
Government agency mortgage-backed securities		470,478		64		(14,234)		456,308		356,858		—		(5,468)		351,390
Government-sponsored enterprises mortgage-backed securities		174,378		134		(6,463)		168,049		178,702		169		(4,130)		174,741
Collateralized mortgage obligations:
Government agency		3,204,890		—		(117,182)		3,087,708		3,367,173		47		(76,746)		3,290,474
Government-sponsored enterprises		742,084		—		(24,601)		717,483		779,911		25		(17,218)		762,718
Debt securities issued by states and political subdivisions		20,477		—		(561)		19,916		20,543		—		(64)		20,479
Total available-for-sale securities	$	5,266,083	$	198	$	(189,515)	$	5,076,766	$	5,357,275	$	241	$	(122,858)	$	5,234,658

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

	March 31, 2018
	Amortized		Fair
(dollars in thousands)	Cost		Value
Due after one year through five years	$	430,259	$	413,492
Due after five years through ten years		223,517		213,810
Due after ten years		20,477		19,916
		674,253		647,218
Government agency mortgage-backed securities		470,478		456,308
Government-sponsored enterprises mortgage-backed securities		174,378		168,049
Collateralized mortgage obligations:
Government agency		3,204,890		3,087,708
Government-sponsored enterprises		742,084		717,483
Total mortgage-backed securities and collateralized mortgage obligations		4,591,830		4,429,548
Total available-for-sale securities	$	5,266,083	$	5,076,766

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

	Time in Continuous Loss as of March 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
U.S. Treasury securities	$	(1,713)	$	47,500	$	(14,702)	$	340,147	$	(16,415)	$	387,647
Government-sponsored enterprises debt securities		(1,299)		58,701		(8,760)		180,954		(10,059)		239,655
Government agency mortgage-backed securities		(6,345)		272,336		(7,889)		140,778		(14,234)		413,114
Government-sponsored enterprises mortgage-backed securities		—		199		(6,463)		162,089		(6,463)		162,288
Collateralized mortgage obligations:
Government agency		(41,628)		1,377,239		(75,554)		1,710,469		(117,182)		3,087,708
Government-sponsored enterprises		(7,092)		338,739		(17,509)		378,744		(24,601)		717,483
Debt securities issued by states and political subdivisions		(561)		19,916		—		—		(561)		19,916
Total available-for-sale securities with unrealized losses	$	(58,638)	$	2,114,630	$	(130,877)	$	2,913,181	$	(189,515)	$	5,027,811

	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