Investment Securities (Tables)

9 Months Ended

Sep. 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:

September 30, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-Sale:
U.S. Treasury notes	$	3,609	$	30	$	—		$	3,639
Obligations of U.S. government agencies	439,488		1,819		(180		)	441,127
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	1,063,642		20,088		(361		)	1,083,369
Private mortgage-backed securities	124		1		(1		)	124
Other investments	4,920		42		—			4,962
Total	$	1,511,783	$	21,980	$	(542	)	$	1,533,221

September 30, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Held-to-Maturity:
State, county and municipal securities	$	165,891	$	6,048	$	(30	)	$	171,909
Corporate securities	53,146		614		(14		)	53,746
Obligations of U.S. government agencies	19,737		315		—			20,052
U.S agency residential mortgage-backed securities &     collateralized mortgage obligations	300,018		14,643		(6,581		)	308,080
Other investments	260		1		—			261
Total	$	539,052	$	21,621	$	(6,625	)	$	554,048

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 September 30,					Nine Months Ended September 30,
	2016			2015		2016			2015
Gross realized gains	$	239		$	23	$	404		$	75
Gross realized losses	(14		)	—		(92		)	—

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 September 30, 2016 and December 31, 2015:

	Less than 12 Months					12 Months or More					Total
September 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	$	—	$	—		$	103,776	$	(180	)	$	103,776	$	(180	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	83,050		(222		)	17,419		(139		)	100,469		(361		)
Private mortgage-backed securities	—		—			50		(1		)	50		(1		)
Total	$	83,050	$	(222	)	$	121,245	$	(320	)	$	204,295	$	(542	)

	Less than 12 Months					12 Months or More					Total
September 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	$	7,746	$	(24	)	$	2,843	$	(6	)	$	10,589	$	(30	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	8,791		(2,721		)	18,523		(3,860		)	27,314		(6,581		)
Corporate securities	5,056		(14		)	—		—			5,056		(14		)
Total	$	21,593	$	(2,759	)	$	21,366	$	(3,866	)	$	42,959	$	(6,625	)

	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 September 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
September 30, 2016	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Within one year	$	340,072	$	345,636	$	99,864	$	97,362
After one year but within five years	1,030,847		1,045,108		290,601		304,804
After five years but within ten years	108,831		109,852		117,829		121,191
After ten years	32,033		32,625		30,758		30,691
Total	$	1,511,783	$	1,533,221	$	539,052	$	554,048