Securities Available for Sale and Held to Maturity (Tables)

3 Months Ended

Mar. 31, 2018

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, 2018 and December 31, 2017 ($ in thousands):

	Securities Available for Sale									Securities Held to Maturity
March 31, 2018	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
Issued by U.S. Government agencies	$	40,838	$	234	$	(954	)	$	40,118	$	—	$	—	$	—		$	—
Issued by U.S. Government sponsored    agencies		254		9		—			263		3,703		73		—			3,776
Obligations of states and political    subdivisions		74,547		548		(82	)		75,013		46,011		706		(87	)		46,630
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		64,707		157		(2,407	)		62,457		12,974		60		(243	)		12,791
Issued by FNMA and FHLMC		789,713		309		(22,346	)		767,676		128,517		60		(3,398	)		125,179
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		977,745		287		(23,495	)		954,537		653,325		154		(20,130	)		633,349
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		201,227		265		(4,059	)		197,433		179,445		171		(3,298	)		176,318
Total	$	2,149,031	$	1,809	$	(53,343	)	$	2,097,497	$	1,023,975	$	1,224	$	(27,156	)	$	998,043
December 31, 2017
U.S. Government agency obligations
Issued by U.S. Government agencies	$	45,508	$	310	$	(800	)	$	45,018	$	—	$	—	$	—		$	—
Issued by U.S. Government sponsored    agencies		255		12		—			267		3,692		182		—			3,874
Obligations of states and political    subdivisions		78,433		850		(54	)		79,229		46,039		1,044		(59	)		47,024
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		66,634		215		(1,103	)		65,746		13,539		207		(73	)		13,673
Issued by FNMA and FHLMC		824,872		827		(11,249	)		814,450		133,975		210		(1,559	)		132,626
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		1,028,176		1,808		(13,194	)		1,016,790		678,926		1,209		(11,065	)		669,070
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		218,252		426		(1,543	)		217,135		180,315		1,102		(1,437	)		179,980
Total	$	2,262,130	$	4,448	$	(27,943	)	$	2,238,635	$	1,056,486	$	3,954	$	(14,193	)	$	1,046,247

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, 2018 and December 31, 2017 ($ in thousands):

	Less than 12 Months					12 Months or More					Total
March 31, 2018	Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses
U.S. Government agency obligations
Issued by U.S. Government agencies	$	5,122	$	(160	)	$	26,702	$	(794	)	$	31,824	$	(954	)
Obligations of states and political subdivisions		18,433		(132	)		3,859		(37	)		22,292		(169	)
Mortgage-backed securities
Residential mortgage pass-through securities
Guaranteed by GNMA		36,439		(1,022	)		31,717		(1,628	)		68,156		(2,650	)
Issued by FNMA and FHLMC		510,587		(12,288	)		347,857		(13,456	)		858,444		(25,744	)
Other residential mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		1,021,035		(20,203	)		506,338		(23,422	)		1,527,373		(43,625	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		275,024		(5,352	)		54,312		(2,005	)		329,336		(7,357	)
Total	$	1,866,640	$	(39,157	)	$	970,785	$	(41,342	)	$	2,837,425	$	(80,499	)
December 31, 2017
U.S. Government agency obligations
Issued by U.S. Government agencies	$	5,214	$	(113	)	$	29,432	$	(687	)	$	34,646	$	(800	)
Obligations of states and political subdivisions		19,345		(80	)		3,874		(33	)		23,219		(113	)
Mortgage-backed securities
Residential mortgage pass-through securities
Guaranteed by GNMA		37,304		(351	)		29,446		(825	)		66,750		(1,176	)
Issued by FNMA and FHLMC		506,410		(4,219	)		369,060		(8,589	)		875,470		(12,808	)
Other residential mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		755,013		(7,668	)		534,955		(16,591	)		1,289,968		(24,259	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		230,898		(1,719	)		55,288		(1,261	)		286,186		(2,980	)
Total	$	1,554,184	$	(14,150	)	$	1,022,055	$	(27,986	)	$	2,576,239	$	(42,136	)

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, 2018, 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	$	28,222	$	28,280	$	155	$	155
Due after one year through five years		54,638		55,290		40,569		41,118
Due after five years through ten years		3,786		3,745		8,990		9,133
Due after ten years		28,993		28,079		—		—
		115,639		115,394		49,714		50,406
Mortgage-backed securities		2,033,392		1,982,103		974,261		947,637
Total	$	2,149,031	$	2,097,497	$	1,023,975	$	998,043