Investment Securities

6 Months Ended

Jun. 30, 2012

Investments, Debt and Equity Securities [Abstract]

Investment Securities

Investment Securities

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

June 30, 2012	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-Sale:
Obligations of U.S. government agencies	$	1,024,769	$	4,259	$	(71	)	$	1,028,957
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	856,395		28,087		(106		)	884,376
Private mortgage-backed securities	645		8		(3		)	650
Total	$	1,881,809	$	32,354	$	(180	)	$	1,913,983

June 30, 2012	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Held-to Maturity:
State, county and municipal securities	$	166,790	$	10,703	$	(97	)	$	177,396
Other securities	136		—		—			136
Total	$	166,926	$	10,703	$	(97	)	$	177,532

December 31, 2011	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-Sale:
Obligations of U.S. government agencies	$	1,134,427	$	4,353	$	(662	)	$	1,138,118
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	848,444		29,567		(14		)	877,997
Private mortgage-backed securities	758		7		(16		)	749
Total	$	1,983,629	$	33,927	$	(692	)	$	2,016,864

December 31, 2011	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Held-to Maturity:
State, county and municipal securities	$	152,619	$	9,113	$	(17	)	$	161,715
Other securities	162		—		—			162
Total	$	152,781	$	9,113	$	(17	)	$	161,877

Gross gains of $201 and gross losses of $3 were realized on the disposition of investment securities during the three months endedJune 30, 2012. Gross gains of $232 and gross losses of $3were realized on the disposition of investment securities during the six months endedJune 30, 2012. Gross gains of $16 and $18 were realized on the disposition of investment securities during the three and six months ended June 30, 2012 and 2011, respectively. No gross losses were realized on the disposition of available-for-sale investment securities during the three and six months ended June 30, 2011.

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, 2012 and December 31, 2011

	Less than 12 Months					12 Months or More					Total
June 30, 2012	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Available-for-Sale:
Obligations of U.S. government agencies	$	64,982	$	(71	)	$	—	$	—		$	64,982	$	(71	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	42,902		(106		)	—		—			42,902		(106		)
Private mortgage-backed securities	226		(1		)	160		(2		)	386		(3		)
Total	$	108,110	$	(178	)	$	160	$	(2	)	$	108,270	$	(180	)

	Less than 12 Months					12 Months or More					Total
June 30, 2012	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Held-to-Maturity:
State, county and municipal securities	$	7,451	$	(80	)	$	721	$	(17	)	$	8,172	$	(97	)

	Less than 12 Months					12 Months or More					Total
December 31, 2011	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Available-for-Sale:
Obligations of U.S. government agencies	$	287,404	$	(662	)	$	—	$	—		$	287,404	$	(662	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	45,694		(14		)	—		—			45,694		(14		)
Private mortgage-backed securities	246		(10		)	177		(6		)	423		(16		)
Total	$	333,344	$	(686	)	$	177	$	(6	)	$	333,521	$	(692	)

	Less than 12 Months				12 Months or More					Total
December 31, 2011	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Held-to-Maturity:
State, county and municipal securities	$	—	$	—	$	773	$	(17	)	$	773	$	(17	)

The investment portfolio is evaluated quarterly for other-than-temporary declines in the market value of each individual investment security. The Company had 29 and 24 individual investment securities that were in an unrealized loss position as of June 30, 2012 and December 31, 2011, respectively. Unrealized losses as of June 30, 2012 and December 31, 2011 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 more likely than not that the Company will not have to sell any such securities before a recovery in cost. No impairment losses were recorded during the three or six months ended June 30, 2012 and 2011.

Maturities of investment securities at June 30, 2012 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, 2012	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Within one year	$	407,085	$	415,903	$	5,827	$	5,676
After one year but within five years	1,194,260		1,210,099		25,859		26,720
After five years but within ten years	186,190		190,628		72,298		76,837
After ten years	94,274		97,353		62,806		68,163
Total	1,881,809		1,913,983		166,790		177,396
Investments with no stated maturity	—		—		136		136
Total	$	1,881,809	$	1,913,983	$	166,926	$	177,532

As of June 30, 2012, the Company had investment securities callable within one year with amortized costs and estimated fair values of $626,027 and $627,832, respectively, including callable structured notes with amortized costs and estimated fair values of $145,265 and $145,698, 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.