Securities (Tables)

6 Months Ended

Jun. 30, 2020

Cash and Cash Equivalents [Abstract]

Summary of Available-for-Sale Securities

A summary of the Company’s available-for-sale securities follows (in thousands):

	June 30, 2020
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
U.S. Treasury securities	$	10,083	$	40	$	(1	)	$	10,122
Obligations of states and political subdivisions		1,836,572		113,757		(50	)		1,950,279
Corporate bonds and other		4,398		171		—			4,569
Residential mortgage-backed securities		1,517,139		54,652		(118	)		1,571,673
Commercial mortgage-backed securities		559,062		23,159		(1	)		582,220
Total securities available-for-sale	$	3,927,254	$	191,779	$	(170	)	$	4,118,863

	June 30, 2019
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
U.S. Treasury securities	$	9,984	$	36	$	—		$	10,020
Obligations of states and political subdivisions		1,103,682		53,593		(61	)		1,157,214
Corporate bonds and other		4,643		51		—			4,694
Residential mortgage-backed securities		1,579,544		19,732		(3,101	)		1,596,175
Commercial mortgage-backed securities		484,919		6,929		(459	)		491,389
Total securities available-for-sale	$	3,182,772	$	80,341	$	(3,621	)	$	3,259,492

	December 31, 2019
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
U.S. Treasury securities	$	9,997	$	22	$	—		$	10,019
Obligations of states and political subdivisions		1,231,619		57,764		(400	)		1,288,983
Corporate bonds and other		4,643		65		—			4,708
Residential mortgage-backed securities		1,586,872		23,139		(1,148	)		1,608,863
Commercial mortgage-backed securities		494,674		6,356		(286	)		500,744
Total securities available-for-sale	$	3,327,805	$	87,346	$	(1,834	)	$	3,413,317

Amortized Cost and Estimated Fair Value of Available-for-Sale Securities

The amortized cost and estimated fair value of available-for-sale securities at June 30, 2020 by contractual and expected maturity, are shown below (in thousands):

	Amortized Cost Basis		Estimated Fair Value
Due within one year	$	128,535	$	129,521
Due after one year through five years		625,856		669,229
Due after five years through ten years		1,079,767		1,148,866
Due after ten years		16,895		17,354
Mortgage-backed securities		2,076,201		2,153,893
Total	$	3,927,254	$	4,118,863

Continuous Unrealized-Loss Position of Available-for-Sale Securities

The following tables disclose the Company’s investment securities that have been in a continuous unrealized-loss position for less than 12 months and for 12 or more months (in thousands):

	Less than 12 Months				12 Months or Longer				Total
June 30, 2020	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. Treasury securities	$	5,055	$	1	$	—	$	—	$	5,055	$	1
Obligations of states and political subdivisions		18,249		50		—		—		18,249		50
Residential mortgage-backed securities		12,590		45		6,454		73		19,044		118
Commercial mortgage-backed securities		4,936		1		—		—		4,936		1
Total	$	40,830	$	97	$	6,454	$	73	$	47,284	$	170

	Less than 12 Months				12 Months or Longer				Total
June 30, 2019	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Obligations of states and political subdivisions	$	—	$	—	$	9,777	$	61	$	9,777	$	61
Residential mortgage-backed securities		17,594		77		404,946		3,024		422,540		3,101
Commercial mortgage-backed securities		—		—		134,881		459		134,881		459
Total	$	17,594	$	77	$	549,604	$	3,544	$	567,198	$	3,621

	Less than 12 Months				12 Months or Longer				Total
December 31, 2019	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Obligations of state and political subdivisions	$	65,787	$	400	$	326	$	—	$	66,113	$	400
Residential mortgage-backed securities		100,004		306		103,983		842		203,987		1,148
Commercial mortgage-backed securities		74,560		178		35,178		108		109,738		286
Total	$	240,351	$	884	$	139,487	$	950	$	379,838	$	1,834