Securities Available for Sale and Held to Maturity (Tables)

6 Months Ended

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

	Securities Available for Sale									Securities Held to Maturity
June 30, 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	$	37,384	$	161	$	(1,131	)	$	36,414	$	3,714	$	89	$	—		$	3,803
Obligations of states and political    subdivisions		64,986		408		(46	)		65,348		42,458		577		(101	)		42,934
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		62,747		124		(2,626	)		60,245		12,756		39		(291	)		12,504
Issued by FNMA and FHLMC		753,124		192		(25,882	)		727,434		123,377		22		(3,979	)		119,420
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		925,705		166		(28,220	)		897,651		627,470		40		(23,956	)		603,554
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		191,538		200		(4,155	)		187,583		176,070		63		(3,710	)		172,423
Total	$	2,035,484	$	1,251	$	(62,060	)	$	1,974,675	$	985,845	$	830	$	(32,037	)	$	954,638
December 31, 2017
U.S. Government agency obligations	$	45,763	$	322	$	(800	)	$	45,285	$	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 June 30, 2018 and December 31, 2017 ($ in thousands):

	Less than 12 Months					12 Months or More					Total
June 30, 2018	Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses
U.S. Government agency obligations	$	5,011	$	(227	)	$	23,844	$	(904	)	$	28,855	$	(1,131	)
Obligations of states and political subdivisions		12,932		(103	)		3,546		(44	)		16,478		(147	)
Mortgage-backed securities
Residential mortgage pass-through securities
Guaranteed by GNMA		33,409		(1,091	)		32,821		(1,826	)		66,230		(2,917	)
Issued by FNMA and FHLMC		503,290		(15,038	)		329,200		(14,823	)		832,490		(29,861	)
Other residential mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		968,691		(25,537	)		497,066		(26,639	)		1,465,757		(52,176	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		280,890		(5,803	)		59,159		(2,062	)		340,049		(7,865	)
Total	$	1,804,223	$	(47,799	)	$	945,636	$	(46,298	)	$	2,749,859	$	(94,097	)
December 31, 2017
U.S. Government agency obligations	$	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	)

Gains and Losses as a Result of Calls and Disposition of Securities

Gross realized gains or losses as a result of calls and dispositions of securities, as well as any associated proceeds, were as follows for the periods presented ($ in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
Available for Sale	2018		2017		2018		2017
Proceeds from calls and sales of securities	$	—	$	26,409	$	—	$	26,409
Gross realized gains		—		1		—		1
Gross realized (losses)		—		—		—		—

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, 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	$	29,282	$	29,393	$	170	$	170
Due after one year through five years		43,102		43,515		40,892		41,326
Due after five years through ten years		3,392		3,331		5,110		5,241
Due after ten years		26,594		25,523		—		—
		102,370		101,762		46,172		46,737
Mortgage-backed securities		1,933,114		1,872,913		939,673		907,901
Total	$	2,035,484	$	1,974,675	$	985,845	$	954,638