Investment Securities (Tables)

6 Months Ended

Jun. 30, 2012

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:

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 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 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	)

Maturities of Investment Securities

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