Securities (Tables)

6 Months Ended

Jun. 30, 2018

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

June 30, 2018	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. Treasury	$	40,098	$	—	$	(2,008	)	$	38,090
U.S. Agencies		200		—		(2	)		198
Mortgage-backed		3,809,164		819		(137,027	)		3,672,956
State and political subdivisions		2,333,242		3,291		(37,561	)		2,298,972
Corporates		1,470		—		(2	)		1,468
Total	$	6,184,174	$	4,110	$	(176,600	)	$	6,011,684

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 June 30, 2018 and December 31, 2017 (in thousands):

	Less than 12 months					12 months or more					Total
June 30, 2018	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Description of Securities
U.S. Treasury	$	9,802	$	(134	)	$	28,288	$	(1,874	)	$	38,090	$	(2,008	)
U.S. Agencies		198		(2	)		—		—			198		(2	)
Mortgage-backed		2,143,258		(57,180	)		1,407,240		(79,847	)		3,550,498		(137,027	)
State and political subdivisions		1,488,089		(20,901	)		341,027		(16,660	)		1,829,116		(37,561	)
Corporates		1,468		(2	)		—		—			1,468		(2	)
Total temporarily-impaired debt securities available for sale	$	3,642,815	$	(78,219	)	$	1,776,555	$	(98,381	)	$	5,419,370	$	(176,600	)

	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 June 30, 2018 and December 31, 2017 (in thousands):

			Gross		Gross
	Amortized		Unrealized		Unrealized			Fair
June 30, 2018	Cost		Gains		Losses			Value
FRB and FHLB stock	$	33,262	$	—	$	—		$	33,262
Other securities – marketable		—		5,018		—			5,018
Other securities – non-marketable		25,532		3,187		(452	)		28,267
Total Other securities	$	58,794	$	8,205	$	(452	)	$	66,547

			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 June 30, 2018 (in thousands):

	Amortized		Fair
	Cost		Value
Due in 1 year or less	$	325,043	$	324,844
Due after 1 year through 5 years		999,207		992,435
Due after 5 years through 10 years		750,393		730,715
Due after 10 years		300,367		290,734
Total		2,375,010		2,338,728
Mortgage-backed securities		3,809,164		3,672,956
Total securities available for sale	$	6,184,174	$	6,011,684

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 June 30, 2018 and December 31, 2017, respectively (in thousands):

			Gross		Gross
	Amortized		Unrealized		Unrealized			Fair
June 30, 2018	Cost		Gains		Losses			Value
State and political subdivisions:
Due in 1 year or less	$	6,919	$	—	$	(52	)	$	6,867
Due after 1 year through 5 years		106,654		226		(9,188	)		97,692
Due after 5 years through 10 years		349,733		3,376		(20,134	)		332,975
Due after 10 years		741,276		5,280		(80,153	)		666,403
Total state and political subdivisions	$	1,204,582	$	8,882	$	(109,527	)	$	1,103,937

			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