Investment Securities (Tables)

9 Months Ended

Sep. 30, 2020

Investments, Debt and Equity Securities [Abstract]

Schedule of Amortized Cost and Fair Values of Investment Securities

The following table presents the amortized cost and estimated fair values of investment securities for the periods presented:

	September 30, 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available for Sale	(in thousands)
State and municipal securities	$	880,495	$	46,216	$	(157)	$	926,554
Corporate debt securities	327,143		16,724		(1,309)		342,558
Collateralized mortgage obligations	516,312		16,207		(46)		532,473
Residential mortgage-backed securities	318,343		3,409		(57)		321,695
Commercial mortgage-backed securities	548,076		24,136		(2)		572,210
Auction rate securities	101,510		—		(3,520)		97,990
Total	$	2,691,879	$	106,692	$	(5,091)	$	2,793,480
Held to Maturity
Residential mortgage-backed securities	$	304,241	$	20,699	$	—	$	324,940

	December 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available for Sale	(in thousands)
State and municipal securities	$	638,125	$	15,826	$	(1,024)	$	652,927
Corporate debt securities	370,401		8,490		(1,534)		377,357
Collateralized mortgage obligations	682,307		11,726		(315)		693,718
Residential mortgage-backed securities	177,183		1,078		(949)		177,312
Commercial mortgage-backed securities	489,603		6,471		(1,777)		494,297
Auction rate securities	107,410		—		(5,484)		101,926
Total	$	2,465,029	$	43,591	$	(11,083)	$	2,497,537
Held to Maturity
Residential mortgage-backed securities	$	369,841	$	13,864	$	—	$	383,705

Schedule of Amortized Cost and Fair Values of Debt Securities by Contractual Maturities

The amortized cost and estimated fair values of debt securities as of September 30, 2020, by contractual maturity, are shown in the following table. Actual maturities may differ from contractual maturities as certain investment securities are subject to call or prepayment with or without call or prepayment penalties.

		September 30, 2020
		Available for Sale				Held to Maturity
		Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(in thousands)
Due in one year or less		$	11,252	$	11,388	$	—	$	—
Due from one year to five years		32,118		33,397		—		—
Due from five years to ten years		315,094		330,233		—		—
Due after ten years		950,684		992,084		—		—
		1,309,148		1,367,102		—		—
Residential mortgage-backed securities(1)		318,343		321,695		304,241		324,940
Commercial mortgage-backed securities(1)		548,076		572,210		—		—
Collateralized mortgage obligations(1)		516,312		532,473		—		—
Total		$	2,691,879	$	2,793,480	$	304,241	$	324,940
(1) Mortgage-backed securities and collateralized mortgage obligations do not have stated maturities and are dependent upon the interest rate environment and prepayments on the underlying loans.

Summary of Gains and Losses from Equity and Debt Securities, and Losses Recognized from Other-than-Temporary Impairment

The following table presents information related to the gross realized gains and losses on the sales of investment securities for the periods presented:

	Gross Realized Gains		Gross Realized Losses		Net Gains
Three months ended	(in thousands)
September 30, 2020	$	94	$	(92)	$	2
September 30, 2019	7,938		(3,446)		4,492
Nine months ended
September 30, 2020	$	6,545	$	(3,492)	$	3,053
September 30, 2019	11,207		(6,474)		4,733

Gross Unrealized Losses and Fair Values of Investments by Category and Length of Time in Continuous Unrealized Loss Position

The following tables present the gross unrealized losses and estimated fair values of investment securities, aggregated by category and length of time that individual securities have been in a continuous unrealized loss position for the periods presented:

	September 30, 2020
	Less than 12 months					12 months or longer					Total
	Number of Securities	Estimated Fair Value		Unrealized Losses		Number of Securities	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
Available for Sale		(in thousands)
State and municipal securities	6	$	25,372	$	(157)	—	$	—	$	—	$	25,372	$	(157)
Corporate debt securities	16	67,030		(965)		1	6,847		(344)		73,877		(1,309)
Collateralized mortgage obligations	1	25,489		(46)		—	—		—		25,489		(46)
Residential mortgage-backed securities	4	75,876		(57)		—	—		—		75,876		(57)
Commercial mortgage-backed securities	1	9,322		(2)		—	—		—		9,322		(2)
Auction rate securities	—	—		—		162	97,990		(3,520)		97,990		(3,520)
Total available for sale(1)	28	$	203,089	$	(1,227)	163	$	104,837	$	(3,864)	$	307,926	$	(5,091)

	December 31, 2019
	Less than 12 months					12 months or longer					Total
	Number of Securities	Estimated Fair Value		Unrealized Losses		Number of Securities	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
Available for Sale	(in thousands)
State and municipal securities	44	$	136,344	$	(1,024)	—	$	—	$	—	$	136,344	$	(1,024)
Corporate debt securities	5	30,719		(346)		8	18,759		(1,188)		49,478		(1,534)
Collateralized mortgage obligations	5	33,865		(190)		1	5,330		(125)		39,195		(315)
Residential mortgage-backed securities	5	12,247		(40)		26	127,373		(909)		139,620		(949)
Commercial mortgage-backed securities	7	121,340		(1,777)		—	—		—		121,340		(1,777)
Auction rate securities	—	—		—		177	101,926		(5,484)		101,926		(5,484)
Total available for sale(1)	66	$	334,515	$	(3,377)	212	$	253,388	$	(7,706)	$	587,903	$	(11,083)