Securities Available for Sale and Held to Maturity (Tables)

6 Months Ended

Jun. 30, 2019

Investments Debt And Equity Securities [Abstract]

Amortized Cost and Estimated Fair Value of Available for Sale and Held to Maturity Securities

The following tables are a summary of the amortized cost and estimated fair value of securities available for sale and held to maturity at June 30, 2019 and December 31, 2018 ($ in thousands):

	Securities Available for Sale									Securities Held to Maturity
June 30, 2019	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. Government agency obligations	$	27,334	$	102	$	(790	)	$	26,646	$	3,758	$	242	$	—		$	4,000
Obligations of states and political    subdivisions		38,203		495		—			38,698		32,860		478		(88	)		33,250
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		66,041		314		(639	)		65,716		11,184		189		(69	)		11,304
Issued by FNMA and FHLMC		628,799		941		(5,376	)		624,364		106,755		379		(430	)		106,704
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		750,605		3,484		(2,718	)		751,371		536,166		6,505		(1,338	)		541,333
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		136,556		683		(309	)		136,930		134,813		1,154		(197	)		135,770
Total	$	1,647,538	$	6,019	$	(9,832	)	$	1,643,725	$	825,536	$	8,947	$	(2,122	)	$	832,361
December 31, 2018
U.S. Government agency obligations	$	31,235	$	109	$	(1,009	)	$	30,335	$	3,736	$	78	$	—		$	3,814
Obligations of states and political    subdivisions		50,503		200		(27	)		50,676		35,783		255		(139	)		35,899
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		69,648		147		(2,301	)		67,494		12,090		45		(257	)		11,878
Issued by FNMA and FHLMC		685,520		127		(18,963	)		666,684		115,133		43		(2,887	)		112,289
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		830,129		67		(18,595	)		811,601		578,827		189		(15,441	)		563,575
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		187,494		191		(2,662	)		185,023		164,074		299		(2,095	)		162,278
Total	$	1,854,529	$	841	$	(43,557	)	$	1,811,813	$	909,643	$	909	$	(20,819	)	$	889,733

Securities with Gross Unrealized Losses, Segregated by Length of Impairment

The tables below include securities with gross unrealized losses segregated by length of impairment at June 30, 2019 and December 31, 2018 ($ in thousands):

	Less than 12 Months					12 Months or More					Total
June 30, 2019	Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses
U.S. Government agency obligations	$	645	$	(1	)	$	22,179	$	(789	)	$	22,824	$	(790	)
Obligations of states and political subdivisions		—		—			8,020		(88	)		8,020		(88	)
Mortgage-backed securities
Residential mortgage pass-through securities
Guaranteed by GNMA		299		(3	)		45,194		(705	)		45,493		(708	)
Issued by FNMA and FHLMC		2,817		(10	)		555,445		(5,796	)		558,262		(5,806	)
Other residential mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		9,392		(75	)		403,393		(3,981	)		412,785		(4,056	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		31,522		(130	)		58,497		(376	)		90,019		(506	)
Total	$	44,675	$	(219	)	$	1,092,728	$	(11,735	)	$	1,137,403	$	(11,954	)
December 31, 2018
U.S. Government agency obligations	$	—	$	—		$	25,045	$	(1,009	)	$	25,045	$	(1,009	)
Obligations of states and political subdivisions		4,954		(9	)		12,802		(157	)		17,756		(166	)
Mortgage-backed securities
Residential mortgage pass-through securities
Guaranteed by GNMA		9,163		(54	)		61,141		(2,504	)		70,304		(2,558	)
Issued by FNMA and FHLMC		31,931		(172	)		731,749		(21,678	)		763,680		(21,850	)
Other residential mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		46,643		(110	)		1,296,221		(33,926	)		1,342,864		(34,036	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		5,497		(37	)		272,789		(4,720	)		278,286		(4,757	)
Total	$	98,188	$	(382	)	$	2,399,747	$	(63,994	)	$	2,497,935	$	(64,376	)

Contractual Maturities of Available for Sale and Held to Maturity Securities

The amortized cost and estimated fair value of securities available for sale and held to maturity at June 30, 2019, by contractual maturity, are shown below ($ in thousands).  Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

	Securities Available for Sale				Securities Held to Maturity
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Due in one year or less	$	29,808	$	29,944	$	180	$	181
Due after one year through five years		8,541		8,646		32,580		32,968
Due after five years through ten years		2,680		2,631		3,858		4,101
Due after ten years		24,508		24,123		—		—
		65,537		65,344		36,618		37,250
Mortgage-backed securities		1,582,001		1,578,381		788,918		795,111
Total	$	1,647,538	$	1,643,725	$	825,536	$	832,361