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

9 Months Ended

Sep. 30, 2017

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, 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

	September 30, 2016
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
U.S. Treasury securities	$	10,685	$	54	$	—		$	10,739
Obligations of U.S. government sponsored enterprises and agencies		114,918		802		—			115,720
Obligations of states and political subdivisions		1,419,737		83,694		(715	)		1,502,716
Corporate bonds and other		68,285		1,325		(1	)		69,609
Residential mortgage-backed securities		750,673		17,125		(1,299	)		766,499
Commercial mortgage-backed securities		259,636		4,200		(89	)		263,747
Total securities available-for-sale	$	2,623,934	$	107,200	$	(2,104	)	$	2,729,030

	December 31, 2016
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
U.S. Treasury securities	$	10,649	$	19	$	—		$	10,668
Obligations of U.S. government sponsored enterprises and agencies		113,450		253		—			113,703
Obligations of states and political subdivisions		1,534,095		40,194		(10,013	)		1,564,276
Corporate bonds and other		51,920		476		(3	)		52,393
Residential mortgage-backed securities		848,614		8,260		(5,513	)		851,361
Commercial mortgage-backed securities		269,044		622		(1,230	)		268,436
Total securities available-for-sale	$	2,827,772	$	49,824	$	(16,759	)	$	2,860,837

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, 2017, by contractual and expected maturity, are shown below (in thousands):

	Amortized Cost Basis		Estimated Fair Value
Due within one year	$	187,370	$	189,136
Due after one year through five years		650,523		679,535
Due after five years through ten years		632,562		656,623
Due after ten years		1,684		2,043
Mortgage-backed securities		1,353,421		1,358,146
Total	$	2,825,560	$	2,885,483

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

The following tables disclose, as of September 30, 2017 and 2016, and December 31, 2016, 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, 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
September 30, 2016	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Obligations of states and political subdivisions	$	82,131	$	711	$	741	$	4	$	82,872	$	715
Corporate bonds and other		12,257		1		—		—		12,257		1
Residential mortgage-backed securities		80,015		267		57,334		1,032		137,349		1,299
Commercial mortgage-backed securities		10,213		25		13,692		64		23,905		89
Total	$	184,616	$	1,004	$	71,767	$	1,100	$	256,383	$	2,104
	Less than 12 Months				12 Months or Longer				Total
December 31, 2016	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Obligations of state and political subdivisions	$	446,052	$	9,997	$	1,209	$	16	$	447,261	$	10,013
Corporate bonds and other		244		3		—		—		244		3
Residential mortgage-backed securities		372,331		4,532		33,227		981		405,558		5,513
Commercial mortgage-backed securities		193,495		1,180		13,263		50		206,758		1,230
Total	$	1,012,122	$	15,712	$	47,699	$	1,047	$	1,059,821	$	16,759