Investment Securities (Tables)

12 Months Ended

Dec. 31, 2016

Investment Securities

Schedule of amortized cost and fair value of securities

	2016								2015
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
(dollars in thousands)	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury securities	$	405,637	$	—	$	(13,164)	$	392,473	$	502,126	$	—	$	(2,150)	$	499,976
Government-sponsored enterprises debt securities		249,707		16		(7,056)		242,667		96,132		16		(324)		95,824
Government agency mortgage-backed securities		190,485		—		(4,822)		185,663		56,490		—		(508)		55,982
Government-sponsored enterprises mortgage-backed securities		208,034		385		(4,034)		204,385		10,185		560		—		10,745
Non-government mortgage-backed securities		—		—		—		—		—		157		—		157
Non-government asset-backed securities		12,592		—		(9)		12,583		95,453		—		(143)		95,310
Collateralized mortgage obligations:
Government agency		3,409,822		794		(58,794)		3,351,822		2,261,526		1,984		(23,576)		2,239,934
Government-sponsored enterprises		700,338		789		(13,206)		687,921		1,046,854		724		(18,241)		1,029,337
Total available-for-sale securities	$	5,176,615	$	1,984	$	(101,085)	$	5,077,514	$	4,068,766	$	3,441	$	(44,942)	$	4,027,265

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

	December 31, 2016
	Amortized		Fair
(dollars in thousands)	Cost		Value
Due after one year through five years	$	254,415	$	247,083
Due after five years through ten years		400,929		388,057
		655,344		635,140
Government agency mortgage-backed securities		190,485		185,663
Government-sponsored enterprises mortgage-backed securities		208,034		204,385
Non-government asset-backed securities		12,592		12,583
Collateralized mortgage obligations:
Government agency		3,409,822		3,351,822
Government-sponsored enterprises		700,338		687,921
Total mortgage- and asset-backed securities		4,521,271		4,442,374
Total available-for-sale securities	$	5,176,615	$	5,077,514

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

	Time in Continuous Loss as of December 31, 2016
	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	$	(13,164)	$	392,473	$	—	$	—	$	(13,164)	$	392,473
Government-sponsored enterprises debt securities		(7,056)		207,651		—		—		(7,056)		207,651
Government agency mortgage-backed securities		(4,822)		185,663		—		—		(4,822)		185,663
Government-sponsored enterprises mortgage-backed securities		(4,034)		195,848		—		—		(4,034)		195,848
Non-government asset-backed securities		(3)		5,202		(6)		7,381		(9)		12,583
Collateralized mortgage obligations:
Government agency		(51,484)		2,847,103		(7,310)		233,706		(58,794)		3,080,809
Government-sponsored enterprises		(1,807)		252,065		(11,399)		279,282		(13,206)		531,347
Total available-for-sale securities with unrealized losses	$	(82,370)	$	4,086,005	$	(18,715)	$	520,369	$	(101,085)	$	4,606,374

	Time in Continuous Loss as of December 31, 2015
	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	$	(2,150)	$	499,976	$	—	$	—	$	(2,150)	$	499,976
Government-sponsored enterprises debt securities		(324)		70,808		—		—		(324)		70,808
Government agency mortgage-backed securities		(508)		55,982		—		—		(508)		55,982
Non-government asset-backed securities		(143)		95,310		—		—		(143)		95,310
Collateralized mortgage obligations:
Government agency		(11,423)		1,428,423		(12,153)		354,335		(23,576)		1,782,758
Government-sponsored enterprises		(3,132)		532,122		(15,109)		354,987		(18,241)		887,109
Total available-for-sale securities with unrealized losses	$	(17,680)	$	2,682,621	$	(27,262)	$	709,322	$	(44,942)	$	3,391,943