Interest-bearing Time Deposits in Banks and Securities (Tables)

9 Months Ended

Sep. 30, 2018

Cash and Cash Equivalents [Abstract]

Summary of Available-for-Sale Securities

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

	September 30, 2018
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
U.S. Treasury Securities	$	9,964	$	—	$	(35	)	$	9,929
Obligations of U.S. government sponsored enterprises and agencies		303		—		(1	)		302
Obligations of states and political subdivisions		1,174,320		21,664		(4,097	)		1,191,887
Corporate bonds and other		4,860		—		(121	)		4,739
Residential mortgage-backed securities		1,533,302		912		(39,908	)		1,494,306
Commercial mortgage-backed securities		453,495		8		(10,299	)		443,204
Total securities available-for-sale	$	3,176,244	$	22,584	$	(54,461	)	$	3,144,367

	September 30, 2017
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
Obligations of U.S. government sponsored enterprises and agencies	$	73,583	$	35	$	(30	)	$	73,588
Obligations of states and political subdivisions		1,379,117		56,671		(1,594	)		1,434,194
Corporate bonds and other		19,439		118		(2	)		19,555
Residential mortgage-backed securities		1,024,615		8,466		(3,797	)		1,029,284
Commercial mortgage-backed securities		328,806		945		(889	)		328,862
Total securities available-for-sale	$	2,825,560	$	66,235	$	(6,312	)	$	2,885,483
	December 31, 2017
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
Obligations of U.S. government sponsored enterprises and agencies	$	60,516	$	—	$	(186	)	$	60,330
Obligations of states and political subdivisions		1,369,295		52,491		(936	)		1,420,850
Corporate bonds and other		11,421		43		(5	)		11,459
Residential mortgage-backed securities		1,223,452		4,561		(8,916	)		1,219,097
Commercial mortgage-backed securities		377,934		263		(2,460	)		375,737
Total securities available-for-sale

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

The amortized cost and estimated fair value of available-for-sale securities at September 30, 2018, by contractual and expected maturity, are shown below (in thousands):

	Amortized Cost Basis		Estimated Fair Value
Due within one year	$	187,577	$	189,177
Due after one year through five years		552,075		565,059
Due after five years through ten years		448,087		450,670
Due after ten years		1,708		1,951
Mortgage-backed securities		1,986,797		1,937,510
Total	$	3,176,244	$	3,144,367

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
September 30, 2018	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. Treasury Securities	$	9,929	$	35	$	—	$	—	$	9,929	$	35
Obligations of U.S. government sponsored enterprises and agencies		302		1		—		—		302		1
Obligations of states and political subdivisions		184,265		2,165		44,750		1,932		229,015		4,097
Corporate bonds and other		4,399		110		449		11		4,848		121
Residential mortgage-backed securities		962,320		20,850		461,227		19,058		1,423,547		39,908
Commercial mortgage-backed securities		270,375		5,908		167,368		4,391		437,743		10,299
Total	$	1,431,590	$	29,069	$	673,794	$	25,392	$	2,105,384	$	54,461
	Less than 12 Months				12 Months or Longer				Total
September 30, 2017	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Obligations of U.S. government sponsored enterprises and agencies	$	45,050	$	30	$	—	$	—	$	45,050	$	30
Obligations of states and political subdivisions		54,983		309		45,217		1,285		100,200		1,594
Corporate bonds and other		—		—		240		2		240		2
Residential mortgage-backed securities		225,369		1,531		131,849		2,266		357,218		3,797
Commercial mortgage-backed securities		170,146		751		21,001		138		191,147		889
Total	$	495,548	$	2,621	$	198,307	$	3,691	$	693,855	$	6,312

	Less than 12 months				12 months or longer				Total
December 31, 2017	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Obligations of U.S. government sponsored enterprises and agencies	$	60,329	$	186	$	—	$	—	$	60,329	$	186
Obligations of state and political subdivisions		66,361		219		44,938		717		111,299		936
Corporate bonds and other		224		2		237		3		461		5
Residential mortgage-backed securities		701,252		3,988		239,641		4,928		940,893		8,916
Commercial mortgage-backed securities		239,548		1,500		92,549		960		332,097		2,460
Total	$	1,067,714	$	5,895	$	377,365	$	6,608	$	1,445,079	$	12,503