Securities Available for Sale and Held to Maturity (Tables)

6 Months Ended

Jun. 30, 2017

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, 2017 and December 31, 2016 ($ in thousands):

	Securities Available for Sale									Securities Held to Maturity
June 30, 2017	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	$	51,431	$	376	$	(530	)	$	51,277	$	—	$	—	$	—		$	—
Issued by U.S. Government sponsored    agencies		256		16		—			272		3,669		153		—			3,822
Obligations of states and political    subdivisions		94,868		1,676		(30	)		96,514		46,098		1,559		(11	)		47,646
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		59,037		294		(909	)		58,422		14,399		235		(62	)		14,572
Issued by FNMA and FHLMC		865,481		1,841		(6,751	)		860,571		144,282		301		(882	)		143,701
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		1,157,006		6,875		(6,640	)		1,157,241		740,042		4,041		(4,563	)		739,520
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		222,226		1,603		(438	)		223,391		191,264		2,234		(474	)		193,024
Total	$	2,450,305	$	12,681	$	(15,298	)	$	2,447,688	$	1,139,754	$	8,523	$	(5,992	)	$	1,142,285
December 31, 2016
U.S. Government agency obligations
Issued by U.S. Government agencies	$	56,272	$	416	$	(925	)	$	55,763	$	—	$	—	$	—		$	—
Issued by U.S. Government sponsored    agencies		257		19		—			276		3,647		355		—			4,002
Obligations of states and political    subdivisions		113,541		1,945		(113	)		115,373		46,303		1,476		(27	)		47,752
Mortgage-backed securities
Residential mortgage pass-through    securities
Guaranteed by GNMA		43,222		340		(776	)		42,786		15,478		280		(52	)		15,706
Issued by FNMA and FHLMC		638,809		1,773		(9,498	)		631,084		81,299		223		(1,084	)		80,438
Other residential mortgage-backed    securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		1,271,198		5,865		(9,112	)		1,267,951		803,474		3,208		(6,519	)		800,163
Commercial mortgage-backed securities
Issued or guaranteed by FNMA,    FHLMC or GNMA		242,869		1,766		(1,186	)		243,449		208,442		1,758		(1,215	)		208,985
Total	$	2,366,168	$	12,124	$	(21,610	)	$	2,356,682	$	1,158,643	$	7,300	$	(8,897	)	$	1,157,046

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, 2017 and December 31, 2016 ($ in thousands):

	Less than 12 Months					12 Months or More					Total
June 30, 2017	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	$	6,701	$	(84	)	$	25,788	$	(446	)	$	32,489	$	(530	)
Obligations of states and political subdivisions		7,166		(26	)		1,315		(15	)		8,481		(41	)
Mortgage-backed securities
Residential mortgage pass-through securities
Guaranteed by GNMA		49,320		(873	)		2,359		(98	)		51,679		(971	)
Issued by FNMA and FHLMC		731,409		(7,632	)		41		(1	)		731,450		(7,633	)
Other residential mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		755,575		(8,683	)		72,249		(2,520	)		827,824		(11,203	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		115,574		(905	)		1,795		(7	)		117,369		(912	)
Total	$	1,665,745	$	(18,203	)	$	103,547	$	(3,087	)	$	1,769,292	$	(21,290	)
December 31, 2016
U.S. Government agency obligations
Issued by U.S. Government agencies	$	9,420	$	(142	)	$	33,248	$	(783	)	$	42,668	$	(925	)
Obligations of states and political subdivisions		20,539		(135	)		654		(5	)		21,193		(140	)
Mortgage-backed securities
Residential mortgage pass-through securities
Guaranteed by GNMA		43,615		(822	)		222		(6	)		43,837		(828	)
Issued by FNMA and FHLMC		588,352		(10,582	)		—		—			588,352		(10,582	)
Other residential mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		1,127,501		(12,722	)		76,196		(2,909	)		1,203,697		(15,631	)
Commercial mortgage-backed securities
Issued or guaranteed by FNMA, FHLMC or    GNMA		244,050		(2,311	)		4,655		(90	)		248,705		(2,401	)
Total	$	2,033,477	$	(26,714	)	$	114,975	$	(3,793	)	$	2,148,452	$	(30,507	)

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

Gains and 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	2017		2016		2017		2016
Proceeds from calls and sales of securities	$	26,409	$	—	$	26,409	$	24,693
Gross realized gains		1		—		1		32
Gross realized (losses)		—		—		—		(342	)

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, 2017, 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	$	28,442	$	28,649	$	155	$	155
Due after one year through five years		75,894		77,675		39,820		41,165
Due after five years through ten years		6,278		6,280		9,792		10,148
Due after ten years		35,941		35,459		—		—
		146,555		148,063		49,767		51,468
Mortgage-backed securities		2,303,750		2,299,625		1,089,987		1,090,817
Total	$	2,450,305	$	2,447,688	$	1,139,754	$	1,142,285