Investment Securities

3 Months Ended

Mar. 31, 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:

March 31, 2012	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-Sale
Obligations of U.S. government agencies	$	1,085,140	$	3,993	$	(687	)	$	1,088,446
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	835,494		30,820		(34		)	866,280
Private mortgage-backed securities	704		11		(5		)	710
Total	$	1,921,338	$	34,824	$	(726	)	$	1,955,436

March 31, 2012	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Held-to Maturity
State, county and municipal securities	$	157,921	$	9,020	$	(158	)	$	166,783
Other securities	149		—		—			149
Total	$	158,070	$	9,020	$	(158	)	$	166,932

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 $31 and $2 were realized on the disposition of available-for-sale securities during the three months ended March 31, 2012 and 2011, respectively. No gross losses were realized on the disposition of available-for-sale investment securities during the three months ended March 31, 2012 or 2011.

The following table shows 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, 2012 and December 31, 2011.

	Less than 12 Months					12 Months or More					Total
March 31, 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	$	177,078	$	(687	)	$	—	$	—		$	177,078	$	(687	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	3,617		(34		)	—		—			3,617		(34		)
Private mortgage-backed securities	—		—			167		(5		)	167		(5		)
Total	$	180,695	$	(721	)	$	167	$	(5	)	$	180,862	$	(726	)

	Less than 12 Months					12 Months or More					Total
March 31, 2012	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Held-to-Maturity
State, county and municipal securities	$	5,501	$	(134	)	$	733	$	(24	)	$	6,234	$	(158	)

	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 27 and 24 individual investment securities that were in an unrealized loss position as of March 31, 2012 and December 31, 2011, respectively. Unrealized losses as of March 31, 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 months ended March 31, 2012 or 2011.

Maturities of investment securities at March 31, 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
March 31, 2012	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Within one year	$	385,624	$	395,736	$	7,023	$	6,799
After one year but within five years	1,312,315		1,328,373		22,288		23,096
After five years but within ten years	146,006		151,084		66,498		70,529
After ten years	77,393		80,243		62,112		66,359
Total	1,921,338		1,955,436		157,921		166,783
Investments with no stated maturity	—		—		149		149
Total	$	1,921,338	$	1,955,436	$	158,070	$	166,932

As of March 31, 2012, the Company had investment securities callable within one year with amortized costs and estimated fair values of $634,320 and $635,629, respectively, including callable structured notes with amortized costs and estimated fair values of $195,257 and $195,899, 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.