Investment Securities (Tables)

12 Months Ended

Dec. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost and Estimated Fair Value of Investment Securities

The amortized cost and estimated fair value of investment securities are summarized below. The majority of securities held are available-for-sale securities with fair value based on quoted prices for similar assets in active markets or quoted prices for identical assets in markets that are not active. Estimated fair values were obtained from an independent pricing service based upon market quotes.

	December 31, 2018
	Amortized Cost		Gross Unrealized Holding Gain		Gross Unrealized Holding Loss			Fair Value		Total Percent
	(Dollars in thousands)
Investment securities available-for-sale:
Residential mortgage-backed securities	$	1,494,106	$	1,348	$	(20,946	)	$	1,474,508		85.03	%
CMO/REMIC - residential		217,223		353		(3,525	)		214,051		12.34	%
Municipal bonds		45,621		332		(1,143	)		44,810		2.59	%
Other securities		716		-		-			716		0.04	%
Total available-for-sale securities	$	1,757,666	$	2,033	$	(25,614	)	$	1,734,085		100.00	%
Investment securities held-to-maturity:
Government agency/GSE	$	138,274	$	572	$	(2,622	)	$	136,224		18.57	%
Residential mortgage-backed securities		153,874		-		(3,140	)		150,734		20.67	%
CMO		215,336		-		(12,081	)		203,255		28.93	%
Municipal bonds		236,956		556		(6,188	)		231,324		31.83	%
Total held-to-maturity securities	$	744,440	$	1,128	$	(24,031	)	$	721,537		100.00	%

	December 31, 2017
	Amortized Cost		Gross Unrealized Holding Gain		Gross Unrealized Holding Loss			Fair Value		Total Percent
	(Dollars in thousands)
Investment securities available-for-sale:
Residential mortgage-backed securities	$	1,747,780	$	11,231	$	(8,102	)	$	1,750,909		84.14	%
CMO/REMIC - residential		274,634		1,277		(2,082	)		273,829		13.16	%
Municipal bonds		54,966		774		(244	)		55,496		2.66	%
Other securities		751		-		-			751		0.04	%
Total available-for-sale securities	$	2,078,131	$	13,282	$	(10,428	)	$	2,080,985		100.00	%
Investment securities held-to-maturity:
Government agency/GSE	$	159,716	$	854	$	(2,134	)	$	158,436		19.25	%
Residential mortgage-backed securities		176,427		667		(382	)		176,712		21.26	%
CMO		225,072		-		(8,641	)		216,431		27.12	%
Municipal bonds		268,675		2,751		(3,790	)		267,636		32.37	%
Total held-to-maturity securities	$	829,890	$	4,272	$	(14,947	)	$	819,215		100.00	%

Summary of Interest Income Earned on Investment Securities

The following table provides information about the amount of interest income earned on investment securities which is fully taxable and which is exempt from regular federal income tax.

	For the Year Ended December 31,
	2018		2017		2016
	(Dollars in thousands)
Investment securities available-for-sale:
Taxable	$	44,423	$	47,596	$	43,538
Tax-advantaged		1,565		2,182		4,164
Total interest income from available-for-sale securities		45,988		49,778		47,702
Investment securities held-to-maturity:
Taxable		11,848		12,558		10,183
Tax-advantaged		7,053		8,457		10,044
Total interest income from held-to-maturity securities		18,901		21,015		20,227
Total interest income from investment securities	$	64,889	$	70,793	$	67,929

Summary of Continuous Unrealized Loss Position of Securities

The tables below show the Company’s investment securities’ gross unrealized losses and fair value by investment category and length of time that individual securities have been in a continuous unrealized loss position at December 31, 2018 and 2017. Management has reviewed individual securities to determine whether a decline in fair value below the amortized cost basis is other-than-temporary. The unrealized losses on these securities were primarily attributed to changes in interest rates. The issuers of these securities have not, to our knowledge, evidenced any cause for default on these securities. These securities have fluctuated in value since their purchase dates as market rates have fluctuated. However, we have the ability and the intention to hold these securities until their fair values recover to cost or maturity. As such, management does not deem these securities to be OTTI.

	December 31, 2018
	Less Than 12 Months					12 Months or Longer					Total
	Fair Value		Gross Unrealized Holding Losses			Fair Value		Gross Unrealized Holding Losses			Fair Value		Gross Unrealized Holding Losses
	(Dollars in thousands)
Investment securities available-for-sale:
Residential mortgage-backed securities	$	692,311	$	(4,864	)	$	593,367	$	(16,082	)	$	1,285,678	$	(20,946	)
CMO/REMIC - residential		36,582		(365	)		135,062		(3,160	)		171,644		(3,525	)
Municipal bonds		9,568		(188	)		14,181		(955	)		23,749		(1,143	)
Total available-for-sale securities	$	738,461	$	(5,417	)	$	742,610	$	(20,197	)	$	1,481,071	$	(25,614	)
Investment securities held-to-maturity:
Government agency/GSE	$	7,479	$	(15	)	$	54,944	$	(2,607	)	$	62,423	$	(2,622	)
Residential mortgage-backed securities		59,871		(484	)		90,863		(2,656	)		150,734		(3,140	)
CMO		-		-			203,254		(12,081	)		203,254		(12,081	)
Municipal bonds		70,989		(778	)		77,723		(5,410	)		148,712		(6,188	)
Total held-to-maturity securities	$	138,339	$	(1,277	)	$	426,784	$	(22,754	)	$	565,123	$	(24,031	)

	December 31, 2017
	Less Than 12 Months					12 Months or Longer					Total
	Fair Value		Gross Unrealized Holding Losses			Fair Value		Gross Unrealized Holding Losses			Fair Value		Gross Unrealized Holding Losses
	(Dollars in thousands)
Investment securities available-for-sale:
Residential mortgage-backed securities	$	414,091	$	(1,828	)	$	303,746	$	(6,274	)	$	717,837	$	(8,102	)
CMO/REMIC - residential		95,137		(487	)		71,223		(1,595	)		166,360		(2,082	)
Municipal bonds		946		(4	)		13,956		(240	)		14,902		(244	)
Total available-for-sale securities	$	510,174	$	(2,319	)	$	388,925	$	(8,109	)	$	899,099	$	(10,428	)
Investment securities held-to-maturity:
Government agency/GSE	$	18,950	$	(27	)	$	43,495	$	(2,107	)	$	62,445	$	(2,134	)
Residential mortgage-backed securities		51,297		(188	)		55,306		(194	)		106,603		(382	)
CMO		-		-			216,431		(8,641	)		216,431		(8,641	)
Municipal bonds		32,069		(492	)		66,217		(3,298	)		98,286		(3,790	)
Total held-to-maturity securities	$	102,316	$	(707	)	$	381,449	$	(14,240	)	$	483,765	$	(14,947	)

Summary of Amortized Cost and Fair Value of Debt Securities by Contractual Maturity

Mortgage-backed and CMO/REMIC securities are included in maturity categories based upon estimated average lives which incorporate estimated prepayment speeds.

	December 31, 2018
	Available-for-sale				Held-to-maturity
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
	(Dollars in thousands)
Due in one year or less	$	13,907	$	14,069	$	500	$	508
Due after one year through five years		1,574,638		1,554,686		288,967		276,693
Due after five years through ten years		143,258		140,500		197,061		193,389
Due after ten years		25,863		24,830		257,912		250,947
Total investment securities	$	1,757,666	$	1,734,085	$	744,440	$	721,537