Investment Securities (Tables)

12 Months Ended

Dec. 31, 2012

Investments, Debt and Equity Securities [Abstract]

Amortized Cost and Approximate Fair Values of Investment Securities

Gross gains of $351 and gross losses of $3 were realized on the disposition of available-for-sale securities in 2012.

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

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

December 31, 2012	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-Sale
Obligations of U.S. government agencies	$	751,501	$	3,518	$	(163	)	$	754,856
U.S. agency residential mortgage-backed securities &    collateralized mortgage obligations	1,214,377		27,000		(1,526		)	1,239,851
Private mortgage-backed securities	539		13		(1		)	551
Total	$	1,966,417	$	30,531	$	(1,690	)	$	1,995,258

December 31, 2012	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Held-to Maturity
State, county and municipal securities	$	192,875	$	10,835	$	(176	)	$	203,534
Corporate securities	14,975		64		(13		)	15,026
Other securities	373		—		—			373
Total	$	208,223	$	10,899	$	(189	)	$	218,933

Gross Unrealized Losses and Fair Values of Investment Securities

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 December 31, 2012 and 2011.

	Less than 12 Months					12 Months or More					Total
December 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	$	93,982	$	(163	)	$	—	$	—		$	93,982	$	(163	)
U.S. agency residential mortgage-backed    securities & collateralized mortgage    obligations	250,198		(1,526		)	—		—			250,198		(1,526		)
Private mortgage-backed securities	—		—			137		(1		)	137		(1		)
Total	$	344,180	$	(1,689	)	$	137	$	(1	)	$	344,317	$	(1,690	)

	Less than 12 Months					12 Months or More					Total
December 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	$	19,389	$	(168	)	$	557	$	(8	)	$	19,946	$	(176	)
Corporate securities	9,312		(13		)	—		—			9,312		(13		)
Total	$	28,701	(181		)	557		(8		)	29,258		(189		)

	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

All other investment securities maturities are shown at contractual maturity dates.

	Available-for-Sale				Held-to-Maturity
December 31, 2012	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Within one year	$	438,770	$	445,319	$	4,657	$	4,657
After one year but within five years	1,042,696		1,056,854		47,437		48,293
After five years but within ten years	351,310		356,641		86,416		90,954
After ten years	133,641		136,444		69,340		74,656
Total	1,966,417		1,995,258		207,850		218,560
Investments with no stated maturity	—		—		373		373
Total	$	1,966,417	$	1,995,258	$	208,223	$	218,933