Investment Securities (Tables)

6 Months Ended

Jun. 30, 2021

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:

	June 30, 2021
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available for Sale	(in thousands)
U.S. Government securities	$	153,885	$	—	$	(340)	$	153,545
U.S. Government sponsored agency securities	62,529		—		(98)		62,431
State and municipal securities	1,002,146		53,924		(608)		1,055,462
Corporate debt securities	354,593		16,876		(88)		371,381
Collateralized mortgage obligations	299,333		7,965		(133)		307,165
Residential mortgage-backed securities	201,654		1,641		(1,748)		201,547
Commercial mortgage-backed securities	858,574		14,338		(1,902)		871,010
Auction rate securities	76,350		—		(1,516)		74,834
Total	$	3,009,064	$	94,744	$	(6,433)	$	3,097,375
Held to Maturity
Residential mortgage-backed securities	$	439,220	$	15,470	$	(5,019)	$	449,671
Commercial mortgage-backed securities	385,063		—		(7,802)		377,261
Total	$	824,283	$	15,470	$	(12,821)	$	826,932

	December 31, 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available for Sale	(in thousands)
State and municipal securities	$	891,327	$	61,286	$	—	$	952,613
Corporate debt securities	348,391		19,445		(691)		367,145
Collateralized mortgage obligations	491,321		12,560		(115)		503,766
Residential mortgage-backed securities	373,779		4,246		(27)		377,998
Commercial mortgage-backed securities	741,172		22,384		(1,141)		762,415
Auction rate securities	101,510		—		(3,304)		98,206
Total	$	2,947,500	$	119,921	$	(5,278)	$	3,062,143
Held to Maturity
Residential mortgage-backed securities	$	278,281	$	18,576	$	—	$	296,857

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 June 30, 2021, 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.

		June 30, 2021
		Available for Sale				Held to Maturity
		Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(in thousands)
Due in one year or less		$	8,212	$	8,240	$	—	$	—
Due from one year to five years		253,200		253,976		—		—
Due from five years to ten years		353,124		371,026		—		—
Due after ten years		1,034,967		1,084,411		—		—
		1,649,503		1,717,653		—		—
Residential mortgage-backed securities(1)		201,654		201,547		439,220		449,671
Commercial mortgage-backed securities(1)		858,574		871,010		385,063		377,261
Collateralized mortgage obligations(1)		299,333		307,165		—		—
Total		$	3,009,064	$	3,097,375	$	824,283	$	826,932
(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)
June 30, 2021	$	465	$	(429)	$	36
June 30, 2020	6,334		(3,329)		3,005
Six months ended
June 30, 2021	$	34,481	$	(970)	$	33,511
June 30, 2020	6,451		(3,400)		3,051

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:

	June 30, 2021
	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)
U.S. Government securities	2	$	153,545	$	(340)	—	$	—	$	—	$	153,545	$	(340)
U.S. Government sponsored agency securities	1	62,431		(98)		—	—		—		62,431		(98)
State and municipal securities	12	46,851		(608)		—	—		—		46,851		(608)
Corporate debt securities	5	19,921		(88)		—	—		—		19,921		(88)
Collateralized mortgage obligations	1	30,402		(133)		—	—		—		30,402		(133)
Residential mortgage-backed securities	7	154,928		(1,748)		—	—		—		154,928		(1,748)
Commercial mortgage-backed securities	15	241,220		(1,902)		—	—		—		241,220		(1,902)
Auction rate securities	—	—		—		118	74,834		(1,516)		74,834		(1,516)
Total available for sale	43	$	709,298	$	(4,917)	118	$	74,834	$	(1,516)	$	784,132	$	(6,433)
Held to Maturity
Residential mortgage-backed securities	12	$	203,077	$	(5,019)	—	$	—	$	—	$	203,077	$	(5,019)
Commercial mortgage-backed securities	21	377,261		(7,802)		—	—		—		377,261		(7,802)
Total	33	$	580,338	$	(12,821)	—	$	—	$	—	$	580,338	$	(12,821)

	December 31, 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)
Corporate debt securities	9	$	44,528	$	(377)	1	$	6,871	$	(314)	$	51,399	$	(691)
Collateralized mortgage obligations	3	57,601		(115)		—	—		—		57,601		(115)
Residential mortgage-backed securities	1	20,124		(27)		—	—		—		20,124		(27)
Commercial mortgage-backed securities	9	144,383		(1,141)		—	—		—		144,383		(1,141)
Auction rate securities	—	—		—		162	98,206		(3,304)		98,206		(3,304)
Total available for sale(1)	22	$	266,636	$	(1,660)	163	$	105,077	$	(3,618)	$	371,713	$	(5,278)

(1) No HTM securities were in an unrealized loss position as of December 31, 2020.