Investment Securities (Tables)

9 Months Ended

Sep. 30, 2013

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:

September 30, 2013	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-Sale:
Obligations of U.S. government agencies	$	792,761	$	1,576	$	(9,862	)	$	784,475
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	1,157,281		14,836		(17,223		)	1,154,894
Private mortgage-backed securities	431		9		(3		)	437
Total	$	1,950,473	$	16,421	$	(27,088	)	$	1,939,806

September 30, 2013	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Held-to-Maturity:
State, county and municipal securities	$	187,202	$	5,011	$	(1,861	)	$	190,352
Corporate securities	18,075		74		(19		)	18,130
Total	$	205,277	$	5,085	$	(1,880	)	$	208,482

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

Realized Gains (Losses) on Investments

Gross realized gains and losses from the disposition of investment securities are summarized in the following table:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2013		2012		2013			2012
Gross realized gains	$	30	$	66	$	42		$	298
Gross realized losses	—		—		(16		)	(3		)

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 September 30, 2013 and December 31, 2012

	Less than 12 Months					12 Months or More					Total
September 30, 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	$	472,232	$	(9,862	)	$	—	$	—		$	472,232	$	(9,862	)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	712,122		(17,223		)	—		—			712,122		(17,223		)
Private mortgage-backed securities	—		—			110		(3		)	110		(3		)
Total	$	1,184,354	$	(27,085	)	$	110	$	(3	)	$	1,184,464	$	(27,088	)

	Less than 12 Months					12 Months or More					Total
September 30, 2013	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Held-to-Maturity:
State, county and municipal securities	$	51,606	$	(1,833	)	$	468	$	(28	)	$	52,074	$	(1,861	)
Corporate securities	7,312		(19		)	—		—			7,312		(19		)
Total	$	58,918	$	(1,852	)	$	468	$	(28	)	$	59,386	$	(1,880	)

	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	)

Maturities of Investment Securities

Maturities of investment securities at September 30, 2013 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
September 30, 2013	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Within one year	$	349,037	$	348,410	$	4,236	$	4,269
After one year but within five years	1,177,551		1,174,066		57,128		57,800
After five years but within ten years	377,332		370,872		85,444		87,378
After ten years	46,553		46,458		58,469		59,035
Total	$	1,950,473	$	1,939,806	$	205,277	$	208,482