Investment Securities (Tables)

3 Months Ended

Mar. 31, 2016

Investment Securities

Amortized cost and estimated fair value by type of investment security

The amortized cost and estimated fair value by type of investment security at March 31, 2016 are as follows:

	Held to Maturity
			Gross		Gross
	Amortized		Unrealized		Unrealized		Estimated		Carrying
	Cost		Gains		Losses		Fair Value		Value
	(Dollars in Thousands)
Other securities	$	2,400	$	—	$	—	$	2,400	$	2,400
Total investment securities	$	2,400	$	—	$	—	$	2,400	$	2,400

	Available for Sale
			Gross		Gross
	Amortized		Unrealized		Unrealized		Estimated		Carrying
	Cost		Gains		Losses		Fair Value		Value(1)
	(Dollars in Thousands)
Residential mortgage-backed securities	$	4,002,441	$	42,217	$	(14,145)	$	4,030,513	$	4,030,513
Obligations of states and political subdivisions		259,908		18,656		(8)		278,556		278,556
Equity securities		28,075		941		(145)		28,871		28,871
Total investment securities	$	4,290,424	$	61,814	$	(14,298)	$	4,337,940	$	4,337,940

(1) Included in the carrying value of residential mortgage-backed securities are $1,119,022 of mortgage-backed securities issued by Ginnie Mae, $2,891,276 of mortgage-backed securities issued by Fannie Mae and Freddie Mac and $20,215issued by non-government entities.

The amortized cost and estimated fair value by type of investment security at December 31, 2015 are as follows:

	Held to Maturity
			Gross		Gross
	Amortized		Unrealized		Unrealized		Estimated		Carrying
	Cost		Gains		Losses		Fair Value		Value
	(Dollars in Thousands)
Other securities	$	2,400	$	—	$	—	$	2,400	$	2,400
Total investment securities	$	2,400	$	—	$	—	$	2,400	$	2,400

	Available for Sale
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair		Carrying
	Cost		Gains		Losses		Value		Value(1)
	(Dollars in Thousands)
Residential mortgage-backed securities	$	3,908,809	$	30,959	$	(46,557)	$	3,893,211	$	3,893,211
Obligations of states and political subdivisions		259,150		18,579		(25)		277,704		277,704
Equity securities		28,075		627		(245)		28,457		28,457
Total investment securities	$	4,196,034	$	50,165	$	(46,827)	$	4,199,372	$	4,199,372

(1) Included in the carrying value of residential mortgage-backed securities are $1,147,143 of mortgage-backed securities issued by Ginnie Mae, $2,724,839 of mortgage-backed securities issued by Fannie Mae and Freddie Mac and $21,229 issued by non-government entities.

Amortized cost and fair value of investment securities, by contractual maturity

	Held to Maturity				Available for Sale
	Amortized		Estimated		Amortized		Estimated
	Cost		Fair Value		Cost		Fair Value
	(Dollars in Thousands)
Due in one year or less	$	1,200	$	1,200	$	—	$	—
Due after one year through five years		1,200		1,200		—		—
Due after five years through ten years		—		—		—		—
Due after ten years		—		—		259,908		278,556
Residential mortgage-backed securities		—		—		4,002,441		4,030,513
Equity securities		—		—		28,075		28,871
Total investment securities	$	2,400	$	2,400	$	4,290,424	$	4,337,940

Gross unrealized losses on investment securities and the related fair value

Gross unrealized losses on investment securities and the fair value of the related securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position at March 31, 2016, were as follows:

	Less than 12 months				12 months or more				Total
			Unrealized				Unrealized				Unrealized
	Fair Value		Losses		Fair Value		Losses		Fair Value		Losses
	(Dollars in Thousands)
Available for sale:
Residential mortgage-backed securities	$	187,800	$	(737)	$	1,287,279	$	(13,408)	$	1,475,079	$	(14,145)
Obligations of states and political subdivisions		1,407		(5)		545		(3)		1,952		(8)
Equity securities		63		(12)		5,617		(133)		5,680		(145)
	$	189,270	$	(754)	$	1,293,441	$	(13,544)	$	1,482,711	$	(14,298)

Gross unrealized losses on investment securities and the fair value of the related securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at December 31, 2015 were as follows:

	Less than 12 months				12 months or more				Total
			Unrealized				Unrealized				Unrealized
	Fair Value		Losses		Fair Value		Losses		Fair Value		Losses
	(Dollars in Thousands)
Available for sale:
Residential mortgage-backed securities	$	1,083,137	$	(9,333)	$	1,454,550	$	(37,224)	$	2,537,687	$	(46,557)
Obligations of states and political subdivisions		6,814		(19)		544		(6)		7,358		(25)
Equity securities		5,041		(35)		5,540		(210)		10,581		(245)
	$	1,094,992	$	(9,387)	$	1,460,634	$	(37,440)	$	2,555,626	$	(46,827)

Reconciliation of credit-related impairment charges on available-for-sale investment

The following table presents a reconciliation of credit-related impairment charges on available-for-sale investments recognized in earnings for the three months ended March 31, 2016 (Dollars in Thousands):

Balance at December 31, 2015	$	13,577
Impairment charges recognized during period		124
Balance at March 31, 2016	$	13,701

The following table presents a reconciliation of credit-related impairment charges on available-for-sale investment recognized in earnings for the three months ended March 31, 2015 (Dollars in Thousands):

Balance at December 31, 2014	$	12,623
Impairment charges recognized during period		227
Balance at March 31, 2015	$	12,850