Securities (Tables)

9 Months Ended

Sep. 30, 2018

This table provides detailed information about securities available for sale at September 30, 2018 and December 31, 2017 (in thousands):

September 30, 2018	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. Treasury	$	40,101	$	—	$	(2,163	)	$	37,938
U.S. Agencies		200		—		(2	)		198
Mortgage-backed		3,778,032		337		(157,991	)		3,620,378
State and political subdivisions		2,323,440		1,419		(50,632	)		2,274,227
Corporates		—		—		—			—
Total	$	6,141,773	$	1,756	$	(210,788	)	$	5,932,741

December 31, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. Treasury	$	40,092	$	—	$	(1,449	)	$	38,643
U.S. Agencies		14,762		—		(10	)		14,752
Mortgage-backed		3,719,369		1,914		(72,040	)		3,649,243
State and political subdivisions		2,546,517		11,965		(15,809	)		2,542,673
Corporates		13,278		—		(12	)		13,266
Total	$	6,334,018	$	13,879	$	(89,320	)	$	6,258,577

Gross Unrealized Losses and Fair Value of Investment Securities Available for Sale

The following table shows the Company’s available for sale investments’ gross unrealized losses and fair value, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at September 30, 2018 and December 31, 2017 (in thousands):

	Less than 12 months					12 months or more					Total
September 30, 2018	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Description of Securities
U.S. Treasury	$	—	$	—		$	37,938	$	(2,163	)	$	37,938	$	(2,163	)
U.S. Agencies		—		—			198		(2	)		198		(2	)
Mortgage-backed		1,700,611		(50,116	)		1,889,126		(107,875	)		3,589,737		(157,991	)
State and political subdivisions		1,426,793		(22,319	)		593,013		(28,313	)		2,019,806		(50,632	)
Corporates		—		—			—		—			—		—
Total temporarily-impaired debt securities available for sale	$	3,127,404	$	(72,435	)	$	2,520,275	$	(138,353	)	$	5,647,679	$	(210,788	)

	Less than 12 months					12 months or more					Total
December 31, 2017	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Description of Securities
U.S. Treasury	$	9,851	$	(64	)	$	28,792	$	(1,385	)	$	38,643	$	(1,449	)
U.S. Agencies		14,553		(10	)		—		—			14,553		(10	)
Mortgage-backed		1,990,006		(19,980	)		1,562,333		(52,060	)		3,552,339		(72,040	)
State and political subdivisions		1,076,930		(7,325	)		376,560		(8,484	)		1,453,490		(15,809	)
Corporates		13,266		(12	)		—		—			13,266		(12	)
Total temporarily-impaired debt securities available for sale	$	3,104,606	$	(27,391	)	$	1,967,685	$	(61,929	)	$	5,072,291	$	(89,320	)

Schedule of Federal Reserve Bank Stock and Federal Home Loan Bank Stock and Other Securities

The table below provides detailed information for FRB stock and Federal Home Loan Bank (FHLB) stock and other securities at September 30, 2018 and December 31, 2017 (in thousands):

			Gross		Gross
	Amortized		Unrealized		Unrealized			Fair
September 30, 2018	Cost		Gains		Losses			Value
FRB and FHLB stock	$	33,262	$	—	$	—		$	33,262
Other securities – marketable		—		5,091		—			5,091
Other securities – non-marketable		23,987		2,914		(2	)		26,899
Total Other securities	$	57,249	$	8,005	$	(2	)	$	65,252

			Gross		Gross
	Amortized		Unrealized		Unrealized			Fair
December 31, 2017	Cost		Gains		Losses			Value
FRB and FHLB stock	$	33,262	$	—	$	—		$	33,262
Other securities – marketable		3		4,637		—			4,640
Other securities – non-marketable		26,606		1,389		—			27,995
Total Other securities	$	59,871	$	6,026	$	—		$	65,897

Available-for-sale Securities [Member]

Contractual Maturity Information

The following table presents contractual maturity information for securities available for sale at September 30, 2018 (in thousands):

	Amortized		Fair
	Cost		Value
Due in 1 year or less	$	327,988	$	327,198
Due after 1 year through 5 years		917,975		906,234
Due after 5 years through 10 years		733,789		708,373
Due after 10 years		383,989		370,558
Total		2,363,741		2,312,363
Mortgage-backed securities		3,778,032		3,620,378
Total securities available for sale	$	6,141,773	$	5,932,741

Held-to-maturity Securities [Member]

Contractual Maturity Information

The following table shows the Company’s held-to-maturity investments’ amortized cost, fair value, and gross unrealized gains and losses at September 30, 2018 and December 31, 2017, respectively (in thousands):

			Gross		Gross
	Amortized		Unrealized		Unrealized			Fair
September 30, 2018	Cost		Gains		Losses			Value
State and political subdivisions:
Due in 1 year or less	$	7,434	$	—	$	(1,027	)	$	6,407
Due after 1 year through 5 years		101,824		237		(9,363	)		92,698
Due after 5 years through 10 years		372,672		4,639		(23,328	)		353,983
Due after 10 years		717,184		5,200		(83,832	)		638,552
Total state and political subdivisions	$	1,199,114	$	10,076	$	(117,550	)	$	1,091,640

			Gross		Gross
	Amortized		Unrealized		Unrealized			Fair
December 31, 2017	Cost		Gains		Losses			Value
State and political subdivisions:
Due in 1 year or less	$	2,275	$	3	$	(24	)	$	2,254
Due after 1 year through 5 years		100,648		3,111		(2,834	)		100,925
Due after 5 years through 10 years		372,234		5,006		(14,117	)		363,123
Due after 10 years		785,857		6,952		(51,664	)		741,145
Total state and political subdivisions	$	1,261,014	$	15,072	$	(68,639	)	$	1,207,447