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

3 Months Ended

Mar. 31, 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):

	March 31, 2018
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
Obligations of U.S. government sponsored enterprises and agencies	$	50,467	$	—	$	(252	)	$	50,215
Obligations of states and political subdivisions		1,289,886		33,014		(2,767	)		1,320,133
Corporate bonds and other		9,382		—		(55	)		9,327
Residential mortgage-backed securities		1,449,482		2,912		(24,622	)		1,427,772
Commercial mortgage-backed securities		476,060		235		(7,549	)		468,746
Total securities available-for-sale	$	3,275,277	$	36,161	$	(35,245	)	$	3,276,193

	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

	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	$	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 March 31, 2018, by contractual and expected maturity, are shown below (in thousands):

	Amortized Cost Basis		Estimated Fair Value
Due within one year	$	228,504	$	230,019
Due after one year through five years		630,063		648,915
Due after five years through ten years		489,472		498,752
Due after ten years		1,696		1,989
Mortgage-backed securities		1,925,542		1,896,518
Total	$	3,275,277	$	3,276,193

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

The following tables disclose, as of March 31, 2018 and 2017, and December 31, 2017, 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, 2018	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Obligations of U.S.government sponsored enterprises and agencies	$	50,215	$	252	$	—	$	—	$	50,215	$	252
Obligations of states and political subdivisions		156,791		1,103		43,335		1,664		200,126		2,767
Corporate bonds and other		9,135		51		235		4		9,370		55
Residential mortgage-backed securities		963,962		16,825		224,777		7,797		1,188,739		24,622
Commercial mortgage-backed securities		319,062		6,056		89,801		1,493		408,863		7,549
Total	$	1,499,165	$	24,287	$	358,148	$	10,958	$	1,857,313	$	35,245

	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
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