Investment Securities (Tables)

12 Months Ended

Dec. 31, 2021

Investments, Debt and Equity Securities [Abstract]

Schedule of Amortized Cost and Fair Values of Investment Securities

The following tables present the amortized cost and estimated fair values of investment securities, as of December 31:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(in thousands)
2021
Available for Sale
U.S. Government securities	$	127,831	$	—	$	(213)	$	127,618
State and municipal securities	1,139,187		50,161		(678)		1,188,670
Corporate debt securities	373,482		13,009		(358)		386,133
Collateralized mortgage obligations	206,532		3,581		(754)		209,359
Residential mortgage-backed securities	231,607		1,224		(3,036)		229,795
Commercial mortgage-backed securities	974,541		6,141		(9,534)		971,148
Auction rate securities	76,350		—		(1,683)		74,667
Total	$	3,129,530	$	74,116	$	(16,256)	$	3,187,390
Held to Maturity
Residential mortgage-backed securities	$	404,958	$	11,022	$	(7,067)	$	408,913
Commercial mortgage-backed securities	575,426		—		(18,472)		556,954
Total	$	980,384	$	11,022	$	(25,539)	$	965,867
2020
Available for Sale
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 December 31, 2021, by contractual maturity, are shown in the following table. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

	Available for Sale				Held to Maturity
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(in thousands)
Due in one year or less	$	9,053	$	9,175	$	—	$	—
Due from one year to five years	163,249		163,924		—		—
Due from five years to ten years	391,040		405,782		—		—
Due after ten years	1,153,508		1,198,207		—		—
	1,716,850		1,777,088		—		—
Residential mortgage-backed securities (1)	231,607		229,795		404,958		408,913
Commercial mortgage-backed securities (1)	974,541		971,148		575,426		556,954
Collateralized mortgage obligations (1)	206,532		209,359		—		—
Total	$	3,129,530	$	3,187,390	$	980,384	$	965,867

(1)     Maturities for mortgage-backed securities and collateralized mortgage obligations are dependent upon the interest rate environment and prepayments on the underlying loans.

Summary of Gains and Losses on the Sales of Securities

The following table presents information related to gross gains and losses on the sales of securities:

	Gross Realized Gains		Gross Realized Losses		Net Gains
	(in thousands)
2021	$	35,593	$	(2,077)	$	33,516
2020	6,545		(3,492)		3,053
2019	11,554		(6,821)		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 investments, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, as of December 31:

	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
2021	(dollars in thousands)
Available for Sale
U.S. Government securities	2	$	127,618	$	(213)	—	$	—	$	—	$	127,618	$	(213)
State and municipal securities	29	82,731		(678)		—	—		—		82,731		(678)
Corporate debt securities	6	43,068		(358)		—	—		—		43,068		(358)
Collateralized mortgage obligations	4	28,517		(754)		—	—		—		28,517		(754)
Residential mortgage-backed securities	7	123,687		(2,388)		1	16,669		(648)		140,356		(3,036)
Commercial mortgage-backed securities	41	512,312		(9,534)		—	—		—		512,312		(9,534)
Auction rate securities	—	—		—		118	74,667		(1,683)		74,667		(1,683)
Total available for sale	89	$	917,933	$	(13,925)	119	$	91,336	$	(2,331)	$	1,009,269	$	(16,256)
Held to Maturity
Residential mortgage-backed securities	14	$	205,969	$	(7,067)	—	$	—	$	—	$	205,969	$	(7,067)
Commercial mortgage-backed securities	36	556,954		(18,472)		—	—		—		556,954		(18,472)
Total	50	$	762,923	$	(25,539)	—	$	—	$	—	$	762,923	$	(25,539)

	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
2020
Available for Sale
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	22	$	266,636	$	(1,660)	163	$	105,077	$	(3,618)	$	371,713	$	(5,278)