Securities Available for Sale and Held to Maturity (Tables)

3 Months Ended

Mar. 31, 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 March 31, 2019 and December 31, 2018 ($ in thousands):

	Securities Available for Sale									Securities Held to Maturity
March 31, 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	$	28,900	$	101	$	(993	)	$	28,008	$	3,747	$	129	$	—		$	3,876
Obligations of states and political    subdivisions		50,660		303		(9	)		50,954		35,352		386		(141	)		35,597
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		67,345		186		(1,355	)		66,176		11,710		102		(128	)		11,684
Issued by FNMA and FHLMC		656,926		418		(11,386	)		645,958		111,962		130		(1,834	)		110,258
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		794,838		388		(10,660	)		784,566		559,690		777		(8,405	)		552,062
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		148,668		254		(1,139	)		147,783		161,858		700		(1,177	)		161,381
Total	$	1,747,337	$	1,650	$	(25,542	)	$	1,723,445	$	884,319	$	2,224	$	(11,685	)	$	874,858
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 March 31, 2019 and December 31, 2018 ($ in thousands):

	Less than 12 Months					12 Months or More					Total
March 31, 2019	Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses
U.S. Government agency obligations	$	—	$	—		$	23,223	$	(993	)	$	23,223	$	(993	)
Obligations of states and political subdivisions		1,366		(6	)		11,095		(144	)		12,461		(150	)
Mortgage-backed securities
Residential mortgage pass-through securities
Guaranteed by GNMA		3,117		(12	)		57,808		(1,471	)		60,925		(1,483	)
Issued by FNMA and FHLMC		16		(1	)		703,426		(13,219	)		703,442		(13,220	)
Other residential mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		4,548		(5	)		1,098,914		(19,060	)		1,103,462		(19,065	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		14,532		(83	)		228,767		(2,233	)		243,299		(2,316	)
Total	$	23,579	$	(107	)	$	2,123,233	$	(37,120	)	$	2,146,812	$	(37,227	)
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 March 31, 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	$	25,576	$	25,599	$	170	$	170
Due after one year through five years		24,719		24,915		34,642		34,891
Due after five years through ten years		3,557		3,501		4,287		4,412
Due after ten years		25,708		24,947		—		—
		79,560		78,962		39,099		39,473
Mortgage-backed securities		1,667,777		1,644,483		845,220		835,385
Total	$	1,747,337	$	1,723,445	$	884,319	$	874,858