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

6 Months Ended

Jun. 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):

	June 30, 2018
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
U.S. Treasury Securities	$	9,957	$	8	$	—		$	9,965
Obligations of U.S. government sponsored enterprises and agencies		304		—		(1	)		303
Obligations of states and political subdivisions		1,257,547		29,924		(2,696	)		1,284,775
Corporate bonds and other		4,861		—		(79	)		4,782
Residential mortgage-backed securities		1,464,345		1,630		(30,718	)		1,435,257
Commercial mortgage-backed securities		471,398		—		(8,913	)		462,485
Total securities available-for-sale	$	3,208,412	$	31,562	$	(42,407	)	$	3,197,567

	June 30, 2017
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
U.S. Treasury securities	$	10,578	$	—	$	(5	)	$	10,573
Obligations of U.S. government sponsored enterprises and agencies		73,666		60		(21	)		73,705
Obligations of states and political subdivisions		1,476,714		58,707		(3,548	)		1,531,873
Corporate bonds and other		30,079		163		(2	)		30,240
Residential mortgage-backed securities		971,557		8,083		(4,558	)		975,082
Commercial mortgage-backed securities		342,651		1,202		(813	)		343,040
Total securities available-for-sale	$	2,905,245	$	68,215	$	(8,947	)	$	2,964,513
	December 31, 2017
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			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	$	3,042,618	$	57,358	$	(12,503	)	$	3,087,473

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, 2018, by contractual and expected maturity, are shown below (in thousands):

	Amortized		Estimated
	Cost Basis		Fair Value
Due within one year	$	183,132	$	184,671
Due after one year through five years		609,481		626,252
Due after five years through ten years		478,355		486,921
Due after ten years		1,701		1,981
Mortgage-backed securities		1,935,743		1,897,742
Total	$	3,208,412	$	3,197,567

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, 2018	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Obligations of U.S. government sponsored enterprises and agencies	$	303	$	1	$	—	$	—	$	303	$	1
Obligations of states and political subdivisions		136,950		1,122		43,239		1,574		180,189		2,696
Corporate bonds and other		4,617		76		233		3		4,850		79
Residential mortgage-backed securities		1,073,327		21,838		227,155		8,880		1,300,482		30,718
Commercial mortgage-backed securities		379,201		7,477		83,285		1,436		462,486		8,913
Total	$	1,594,398	$	30,514	$	353,912	$	11,893	$	1,948,310	$	42,407

	Less than 12 Months				12 Months or Longer				Total
June 30, 2017	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. Treasury securities	$	10,321	$	5	$	—	$	—	$	10,321	$	5
Obligations of U.S. government sponsored enterprises and agencies		30,062		21		—		—		30,062		21
Obligations of states and political subdivisions		110,706		1,906		37,851		1,642		148,557		3,548
Corporate bonds and other		241		2		—		—		241		2
Residential mortgage-backed securities		422,087		3,387		60,410		1,171		482,497		4,558
Commercial mortgage-backed securities		150,805		745		20,120		68		170,925		813
Total	$	724,222	$	6,066	$	118,381	$	2,881	$	842,603	$	8,947

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