Investment Securities (Tables)

6 Months Ended

Jun. 30, 2018

Investment Securities

Schedule of amortized cost and fair value of securities

	June 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	$	403,744	$	—	$	(17,687)	$	386,057	$	404,376	$	—	$	(12,121)	$	392,255
Government-sponsored enterprises debt securities		249,714		—		(11,187)		238,527		249,712		—		(7,111)		242,601
Government agency mortgage-backed securities		455,769		—		(16,919)		438,850		356,858		—		(5,468)		351,390
Government-sponsored enterprises mortgage-backed securities		168,151		109		(7,019)		161,241		178,702		169		(4,130)		174,741
Collateralized mortgage obligations:
Government agency		3,057,867		—		(133,061)		2,924,806		3,367,173		47		(76,746)		3,290,474
Government-sponsored enterprises		700,900		—		(27,646)		673,254		779,911		25		(17,218)		762,718
Debt securities issued by states and political subdivisions		20,411		—		(595)		19,816		20,543		—		(64)		20,479
Total available-for-sale securities	$	5,056,556	$	109	$	(214,114)	$	4,842,551	$	5,357,275	$	241	$	(122,858)	$	5,234,658

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

	June 30, 2018
	Amortized		Fair
(dollars in thousands)	Cost		Value
Due after one year through five years	$	478,744	$	458,717
Due after five years through ten years		174,714		165,867
Due after ten years		20,411		19,816
		673,869		644,400
Government agency mortgage-backed securities		455,769		438,850
Government-sponsored enterprises mortgage-backed securities		168,151		161,241
Collateralized mortgage obligations:
Government agency		3,057,867		2,924,806
Government-sponsored enterprises		700,900		673,254
Total mortgage-backed securities and collateralized mortgage obligations		4,382,687		4,198,151
Total available-for-sale securities	$	5,056,556	$	4,842,551

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

	Time in Continuous Loss as of June 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	$	(1,963)	$	47,287	$	(15,724)	$	338,770	$	(17,687)	$	386,057
Government-sponsored enterprises debt securities		(1,700)		58,300		(9,487)		180,227		(11,187)		238,527
Government agency mortgage-backed securities		(8,499)		304,708		(8,420)		134,142		(16,919)		438,850
Government-sponsored enterprises mortgage-backed securities		(1)		189		(7,018)		155,708		(7,019)		155,897
Collateralized mortgage obligations:
Government agency		(42,264)		1,162,582		(90,796)		1,762,224		(133,060)		2,924,806
Government-sponsored enterprises		(7,362)		272,911		(20,285)		400,343		(27,647)		673,254
Debt securities issued by states and political subdivisions		(595)		19,816		—		—		(595)		19,816
Total available-for-sale securities with unrealized losses	$	(62,384)	$	1,865,793	$	(151,730)	$	2,971,414	$	(214,114)	$	4,837,207

	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