Investment Securities (Tables)

3 Months Ended

Mar. 31, 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:

March 31, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-Sale:
U.S. Treasury notes	$	3,911	$	24	$	—		$	3,935
Obligations of U.S. government agencies	530,037		1,719		(324		)	531,432
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	1,010,675		14,550		(862		)	1,024,363
Private mortgage-backed securities	144		1		(2		)	143
Other investments	3,450		27		—			3,477
Total	$	1,548,217	$	16,321	$	(1,188	)	$	1,563,350

March 31, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Held-to-Maturity:
State, county and municipal securities	$	167,975	$	5,553	$	(14	)	$	173,514
Corporate securities	51,918		292		(61		)	52,149
U.S agency residential mortgage-backed securities &     collateralized mortgage obligations	341,434		11,640		(5,145		)	347,929
Obligations of U.S. government agencies	19,737		248		—			19,985
Other investments	326		1		—			327
Total	$	581,390	$	17,734	$	(5,220	)	$	593,904

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
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	356,742		7,686		(5,420		)	359,008
Obligations of U.S. government agencies	19,738		—		(102		)	19,636
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 March 31,
	2016			2015
Gross realized gains	$	57		$	6
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 March 31, 2016 and December 31, 2015.

	Less than 12 Months					12 Months or More					Total
March 31, 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	$	118,698	$	(226	)	$	35,355	$	(98	)	$	154,053	$	(324	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	146,840		(586		)	25,708		(276		)	172,548		(862		)
Private mortgage-backed securities	—		—			57		(2		)	57		(2		)
Other investments	—		—			—		—			—		—
Total	$	265,538	$	(812	)	$	61,120	$	(376	)	$	326,658	$	(1,188	)

	Less than 12 Months					12 Months or More					Total
March 31, 2016	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Held-to-Maturity:
State, county and municipal securities	$	3,379	$	(7	)	$	3,606	$	(7	)	$	6,985	$	(14	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	13,801		(4,364		)	24,049		(781		)	37,850		(5,145		)
Corporate securities	10,049		(61		)	—		—			10,049		(61		)
Total	$	27,229	$	(4,432	)	$	27,655	$	(788	)	$	54,884	$	(5,220	)

	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	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	67,295		(4,288		)	69,539		(1,132		)	136,834		(5,420		)
Obligations of U.S. government agencies	19,738		(102		)	—		—			19,738		(102		)
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 March 31, 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
March 31, 2016	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Within one year	$	317,502	$	320,927	$	87,930	$	90,154
After one year but within five years	1,089,290		1,099,333		328,090		333,231
After five years but within ten years	70,534		71,242		125,412		128,977
After ten years	70,891		71,848		39,958		41,542
Total	$	1,548,217	$	1,563,350	$	581,390	$	593,904