Investment Securities (Tables)

9 Months Ended

Sep. 30, 2017

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 September 30, 2017 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	$	4,031,240	$	21,637	$	(41,311)	$	4,011,566	$	4,011,566
Obligations of states and political subdivisions		231,262		9,393		(109)		240,546		240,546
Equity securities		28,075		357		(356)		28,076		28,076
Total investment securities	$	4,290,577	$	31,387	$	(41,776)	$	4,280,188	$	4,280,188

(1) Included in the carrying value of residential mortgage-backed securities are $700,593 of mortgage-backed securities issued by Ginnie Mae and $3,310,973 of mortgage-backed securities issued by Fannie Mae and Freddie Mac.

The amortized cost and estimated fair value by type of investment security at December 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		Estimated
	Amortized		unrealized		unrealized		fair		Carrying
	cost		gains		losses		value		value(1)
	(Dollars in Thousands)
Residential mortgage-backed securities	$	3,946,144	$	18,246	$	(69,920)	$	3,894,470	$	3,894,470
Obligations of states and political subdivisions		244,622		10,783		(433)		254,972		254,972
Equity securities		28,075		314		(482)		27,907		27,907
Total investment securities	$	4,218,841	$	29,343	$	(70,835)	$	4,177,349	$	4,177,349

(1) Included in the carrying value of residential mortgage-backed securities are $850,033 of mortgage-backed securities issued by Ginnie Mae, $3,026,832 of mortgage-backed securities issued by Fannie Mae and Freddie Mac and $17,605 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	$	1,075	$	1,075	$	—	$	—
Due after one year through five years		1,325		1,325		—		—
Due after five years through ten years		—		—		1,939		1,990
Due after ten years		—		—		229,323		238,556
Residential mortgage-backed securities		—		—		4,031,240		4,011,566
Equity securities		—		—		28,075		28,076
Total investment securities	$	2,400	$	2,400	$	4,290,577	$	4,280,188

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 September 30, 2017, 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	$	2,026,450	$	(24,622)	$	857,381	$	(16,689)	$	2,883,831	$	(41,311)
Obligations of states and political subdivisions		12,612		(101)		524		(8)		13,136		(109)
Equity securities		16,743		(257)		2,151		(99)		18,894		(356)
	$	2,055,805	$	(24,980)	$	860,056	$	(16,796)	$	2,915,861	$	(41,776)

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, 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	$	2,513,872	$	(52,245)	$	396,695	$	(17,675)	$	2,910,567	$	(69,920)
Obligations of states and political subdivisions		31,104		(433)		—		—		31,104		(433)
Equity securities		14,066		(184)		5,452		(298)		19,518		(482)
	$	2,559,042	$	(52,862)	$	402,147	$	(17,973)	$	2,961,189	$	(70,835)

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

The following tables present a reconciliation of credit-related impairment charges on available-for-sale investment recognized in earnings for the nine months ended September 30, 2017 and the three and nine months ended September 30, 2016 (Dollars in Thousands):

Balance at December 31, 2016	$	13,931
Sale of other-than-temporarily impaired available-for-sale securities during period		(13,931)
Balance at September 30, 2017	$	—

Balance at June 30, 2016	$	13,768
Impairment charges recognized during period		90
Balance at September 30, 2016	$	13,858

Balance at December 31, 2015	$	13,577
Impairment charges recognized during period		281
Balance at September 30, 2016	$	13,858