Investment Securities (Tables)

6 Months Ended

Jun. 30, 2016

Investments, Debt and Equity Securities [Abstract]

Amortized Cost and Approximate Fair Values of Investment Securities

The amortized cost and approximate fair values of investment securities are summarized as follows:

June 30, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-Sale:
U.S. Treasury notes	$	3,909	$	44	$	—		$	3,953
Obligations of U.S. government agencies	450,544		2,882		(21		)	453,405
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	1,022,462		22,252		(117		)	1,044,597
Private mortgage-backed securities	136		1		(2		)	135
Other investments	3,450		41		—			3,491
Total	$	1,480,501	$	25,220	$	(140	)	$	1,505,581

June 30, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Held-to-Maturity:
State, county and municipal securities	$	164,334	$	7,024	$	(1	)	$	171,357
Corporate securities	51,262		580		—			51,842
Obligations of U.S. government agencies	19,737		483		—			20,220
U.S agency residential mortgage-backed securities &     collateralized mortgage obligations	320,620		15,925		(5,777		)	330,768
Other investments	294		1		—			295
Total	$	556,247	$	24,013	$	(5,778	)	$	574,482

December 31, 2015	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-Sale:
U.S. Treasury notes	$	3,912	$	3	$	(4	)	$	3,911
Obligations of U.S. government agencies	521,079		712		(1,610		)	520,181
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	921,699		9,448		(2,101		)	929,046
Private mortgage-backed securities	156		1		(1		)	156
Other investments	3,550		5		(9		)	3,546
Total	$	1,450,396	$	10,169	$	(3,725	)	$	1,456,840

December 31, 2015	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Held-to-Maturity:
State, county and municipal securities	$	173,785	$	5,103	$	(227	)	$	178,661
Corporate securities	50,046		64		(220		)	49,890
Obligations of U.S. government agencies	19,738		—		(102		)	19,636
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	356,742		7,686		(5,420		)	359,008
Other investments	354		1		—			355
Total	$	600,665	$	12,854	$	(5,969	)	$	607,550

Realized Gains (Losses) on Investments

Gross realized gains and losses from the disposition of investment securities are summarized in the following table:

	Three Months Ended June 30,				Six Months Ended June 30,
	2016		2015		2016			2015
Gross realized gains	$	108	$	46	$	165		$	52
Gross realized losses	—		—		(78		)	—

Gross Unrealized Losses and Fair Values of Investment Securities

The following tables show the gross unrealized losses and fair values of investment securities, aggregated by investment category, and the length of time individual investment securities have been in a continuous unrealized loss position, as of June 30, 2016 and December 31, 2015:

	Less than 12 Months					12 Months or More					Total
June 30, 2016	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Available-for-Sale:
Obligations of U.S. government agencies	$	—	$	—		$	10,477	$	(21	)	$	10,477	$	(21	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	11,097		(41		)	18,609		(76		)	29,706		(117		)
Private mortgage-backed securities	—		—			54		(2		)	54		(2		)
Total	$	11,097	$	(41	)	$	29,140	$	(99	)	$	40,237	$	(140	)

	Less than 12 Months					12 Months or More					Total
June 30, 2016	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Held-to-Maturity:
State, county and municipal securities	$	625	$	—		$	2,233	$	(1	)	$	2,858	$	(1	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	5,030		(2,631		)	20,683		(3,146		)	25,713		(5,777		)
Total	$	5,655	$	(2,631	)	$	22,916	$	(3,147	)	$	28,571	$	(5,778	)

	Less than 12 Months					12 Months or More					Total
December 31, 2015	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Available-for-Sale:
U.S. Treasury notes	$	2,092	$	(4	)	$	—	$	—		$	2,092	$	(4	)
Obligations of U.S. government agencies	209,631		(1,077		)	54,619		(533		)	264,250		(1,610		)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	343,875		(1,577		)	28,010		(524		)	371,885		(2,101		)
Private mortgage-backed securities	—		—			61		(1		)	61		(1		)
Other investments	1,225		(9		)	—		—			1,225		(9		)
Total	$	556,823	$	(2,667	)	$	82,690	$	(1,058	)	$	639,513	$	(3,725	)

	Less than 12 Months					12 Months or More					Total
December 31, 2015	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Held-to-Maturity:
State, county and municipal securities	$	10,182	$	(39	)	$	9,476	$	(188	)	$	19,658	$	(227	)
Obligations of U.S. government agencies	19,738		(102		)	—		—			19,738		(102		)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	67,295		(4,288		)	69,539		(1,132		)	136,834		(5,420		)
Corporate securities	31,135		(220		)	—		—			31,135		(220		)
Total	$	128,350	$	(4,649	)	$	79,015	$	(1,320	)	$	207,365	$	(5,969	)

Maturities of Investment Securities

Maturities of investment securities at June 30, 2016 are shown below. Maturities of mortgage-backed securities have been adjusted to reflect shorter maturities based upon estimated prepayments of principal. All other investment securities maturities are shown at contractual maturity dates.

	Available-for-Sale				Held-to-Maturity
June 30, 2016	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Within one year	$	352,031	$	358,337	$	90,746	$	94,029
After one year but within five years	1,049,286		1,066,900		311,641		319,471
After five years but within ten years	58,599		59,317		128,607		134,596
After ten years	20,585		21,027		25,253		26,386
Total	$	1,480,501	$	1,505,581	$	556,247	$	574,482