Investment Securities

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



June 30, 2014	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-Sale:
Obligations of U.S. government agencies	$	722,034	$	1,707	$	(5,174	)	$	718,567
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	778,641		12,806		(3,383		)	788,064
Private mortgage-backed securities	361		6		(2		)	365
Total	$	1,501,036	$	14,519	$	(8,559	)	$	1,506,996



June 30, 2014	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Held-to-Maturity:
State, county and municipal securities	$	179,131	$	6,159	$	(600	)	$	184,690
Corporate securities	17,908		116		—			18,024
U.S agency residential mortgage-backed securities & collateralized mortgage obligations	389,950		18		—			389,968
Total	$	586,989	$	6,293	$	(600	)	$	592,682



December 31, 2013	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-Sale:
Obligations of U.S. government agencies	$	774,055	$	1,432	$	(12,249	)	$	763,238
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	1,197,295		11,905		(25,147		)	1,184,053
Private mortgage-backed securities	407		9		(1		)	415
Total	$	1,971,757	$	13,346	$	(37,397	)	$	1,947,706



December 31, 2013	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Held-to-Maturity:
State, county and municipal securities	$	185,818	$	4,043	$	(2,049	)	$	187,812
Corporate securities	18,019		103		(8		)	18,114
Total	$	203,837	$	4,146	$	(2,057	)	$	205,926

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,
	2014		2013		2014		2013
Gross realized gains	$	18	$	4	$	243	$	12
Gross realized losses	1		16		155		16

On June 27, 2014, the Company transferred available-for-sale U.S. agency residential mortgage-backed securities and collateralized mortgage obligations with amortized costs and fair values of $396,640 and $388,808, respectively, into the held-to-maturity category. Unrealized net losses of $7,832 included in accumulated other comprehensive income at the time of the transfer are being amortized to yield over the remaining expected lives of the transferred securities of 4.3 years.

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, 2014 and December 31, 2013.



	Less than 12 Months					12 Months or More					Total
June 30, 2014	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Available-for-Sale:
Obligations of U.S. government agencies	$	61,265	$	(185	)	$	353,997	$	(4,989	)	$	415,262	$	(5,174	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	47,884		(146		)	203,157		(3,237		)	251,041		(3,383		)
Private mortgage-backed securities	—		—			95		(2		)	95		(2		)
Total	$	109,149	$	(331	)	$	557,249	$	(8,228	)	$	666,398	$	(8,559	)



	Less than 12 Months					12 Months or More					Total
June 30, 2014	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Held-to-Maturity:
State, county and municipal securities	$	267	$	(1	)	$	28,986	$	(599	)	$	29,253	$	(600	)
Total	$	267	$	(1	)	$	28,986	$	(599	)	$	29,253	$	(600	)



	Less than 12 Months					12 Months or More					Total
December 31, 2013	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Available-for-Sale:
Obligations of U.S. government agencies	$	458,385	$	(10,355	)	$	59,362	$	(1,894	)	$	517,747	$	(12,249	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	634,199		(17,273		)	166,930		(7,874		)	801,129		(25,147		)
Private mortgage-backed securities	—		—			104		(1		)	104		(1		)
Total	$	1,092,584	$	(27,628	)	$	226,396	$	(9,769	)	$	1,318,980	$	(37,397	)



	Less than 12 Months					12 Months or More					Total
December 31, 2013	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Held-to-Maturity:
State, county and municipal securities	$	37,550	$	(1,319	)	$	14,296	$	(730	)	$	51,846	$	(2,049	)
Corporate securities	7,294		(8		)	—		—			7,294		(8		)
Total	$	44,844	$	(1,327	)	$	14,296	$	(730	)	$	59,140	$	(2,057	)

The investment portfolio is evaluated quarterly for other-than-temporary declines in the market value of each individual investment security. The Company had 106 and 229 individual investment securities that were in an unrealized loss position as of June 30, 2014 and December 31, 2013, respectively. Unrealized losses as of June 30, 2014 and December 31, 2013 related primarily to fluctuations in the current interest rates. The Company does not have the intent to sell any of the available-for-sale securities in the above table and it is not likely that the Company will have to sell any such securities before a recovery in cost. No impairment losses were recorded during the three and six months ended June 30, 2014 and 2013.

Maturities of investment securities at June 30, 2014 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, 2014	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Within one year	$	235,880	$	238,377	$	75,137	$	75,805
After one year but within five years	1,046,202		1,050,653		262,721		265,277
After five years but within ten years	203,374		202,197		174,980		176,267
After ten years	15,580		15,769		74,151		75,333
Total	$	1,501,036	$	1,506,996	$	586,989	$	592,682

As of June 30, 2014, the Company had investment securities callable within one year with amortized costs and estimated fair values of $208,708 and $208,188, respectively, including callable structured notes with amortized costs and estimated fair values of $94,473 and $94,487, respectively. These investment securities are primarily classified as available-for-sale and included in the after one year but within five years category in the table above.