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

3 Months Ended

Mar. 31, 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):

	March 31, 2017
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
U.S. Treasury securities	$	10,614	$	5	$	—		$	10,619
Obligations of U.S. government sponsored enterprises and agencies		79,777		130		(2	)		79,905
Obligations of states and political subdivisions		1,524,010		47,902		(7,399	)		1,564,513
Corporate bonds and other		47,601		333		(3	)		47,931
Residential mortgage-backed securities		989,272		7,718		(5,437	)		991,553
Commercial mortgage-backed securities		324,716		561		(1,519	)		323,758
Total securities available-for-sale	$	2,975,990	$	56,649	$	(14,360	)	$	3,018,279

	March 31, 2016
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
U.S. Treasury securities	$	10,756	$	73	$	—		$	10,829
Obligations of U.S. government sponsored enterprises and agencies		131,484		1,061		—			132,545
Obligations of states and political subdivisions		1,388,369		82,693		(28	)		1,471,034
Corporate bonds and other		68,836		1,896		—			70,732
Residential mortgage-backed securities		793,509		17,180		(963	)		809,726
Commercial mortgage-backed securities		264,231		4,013		(71	)		268,173
Total securities available-for-sale	$	2,657,185	$	106,916	$	(1,062	)	$	2,763,039

	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 March 31, 2017, by contractual and expected maturity, are shown below (in thousands):

	Amortized Cost Basis		Estimated Fair Value
Due within one year	$	195,694	$	197,227
Due after one year through five years		671,223		697,730
Due after five years through ten years		793,021		805,607
Due after ten years		2,064		2,404
Mortgage-backed securities		1,313,988		1,315,311
Total	$	2,975,990	$	3,018,279

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

The following tables disclose, as of March 31, 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
March 31, 2017	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Obligations of U.S.government sponsored enterprises and agencies	$	10,008	$	2	$	—	$	—	$	10,008	$	2
Obligations of states and political subdivisions		259,419		7,391		1,215		8		260,634		7,399
Corporate bonds and other		9,001		3		—		—		9,001		3
Residential mortgage-backed securities		494,836		4,544		31,558		893		526,394		5,437
Commercial mortgage-backed securities		225,789		1,454		12,788		65		238,577		1,519
Total	$	999,053	$	13,394	$	45,561	$	966	$	1,044,614	$	14,360
	Less than 12 Months				12 Months or Longer				Total
March 31, 2016	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Obligations of states and political subdivisions	$	6,804	$	23	$	1,071	$	5	$	7,875	$	28
Residential mortgage-backed securities		25,152		357		48,124		606		73,276		963
Commercial mortgage-backed securities		15,553		13		14,520		58		30,073		71
Total	$	47,509	$	393	$	63,715	$	669	$	111,224	$	1,062
	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