Borrowed Funds (Details) (USD $)	1 Months Ended	12 Months Ended		1 Months Ended				1 Months Ended	12 Months Ended		12 Months Ended			12 Months Ended			1 Months Ended		12 Months Ended
	Jan. 31, 2009	Dec. 31, 2011	Dec. 31, 2010	Oct. 31, 2009 Federal Home Loan Bank Advances [Member]	Dec. 31, 2011 Federal Home Loan Bank Advances [Member]	Dec. 31, 2010 Federal Home Loan Bank Advances [Member]	Jan. 31, 2009 Federal Home Loan Bank Advances [Member]	Feb. 28, 2007 Subordinated Notes Payable [Member]	Dec. 31, 2011 Subordinated Notes Payable [Member]	Dec. 31, 2010 Subordinated Notes Payable [Member]	Dec. 31, 2011 Trust II [Member]	Dec. 31, 2004 Trust II [Member]	Dec. 31, 2010 Trust II [Member]	Dec. 31, 2011 Trust II [Member] Junior Subordinated Deferrable Interest Debentures [Member]	Dec. 31, 2010 Trust II [Member] Junior Subordinated Deferrable Interest Debentures [Member]	Dec. 31, 2004 Trust II [Member] Junior Subordinated Deferrable Interest Debentures [Member]	Jul. 31, 2010 Summit Trust [Member]	Aug. 31, 2011 Frost Bank [Member] Subordinated Notes Payable [Member]	Dec. 31, 2010 Maximum [Member] Federal Funds Purchased [Member]	Dec. 31, 2010 Maximum [Member] Securities Sold Under Agreements To Repurchase [Member]	Dec. 31, 2010 Minimum [Member] Federal Funds Purchased [Member]	Dec. 31, 2010 Minimum [Member] Securities Sold Under Agreements To Repurchase [Member]	Jan. 31, 2009 Variable Rate One [Member] Federal Home Loan Bank Advances [Member]	Jan. 31, 2009 Variable Rate Two [Member] Federal Home Loan Bank Advances [Member]	Jan. 31, 2009 Variable Rate Three [Member] Federal Home Loan Bank Advances [Member]
Borrowed Funds [Line Items]
Federal home loan bank advances					$ 26,000	$ 45,000
Debt instrument maturity period, days																			90	90	1	30
Federal home loan bank advances, weighted-average rate					6.00%	6.00%
Aggregate borrowed funds							230,000,000																30,000,000	100,000,000	100,000,000
LIBOR plus margin	three-month LIBOR plus a margin of 0.36%							three-month LIBOR for the related interest period plus 0.53%				three-month LIBOR plus a margin of 1.55%					three-month LIBOR plus a margin of 2.65%
Prepayment penalty				1,400,000
Swap fixed interest rate to be paid				2.85%
Interest rate swaps and recognized gains				17,700,000
Federal funds purchased		875,000	2,000,000
Securities sold under agreements to repurchase		721,300,000	473,700,000
Subordinated notes, issued								100,000,000
Redemption of Subordinated notes																		150,000,000
Subordinated notes, interest rate								5.75%										6.875%
Subordinated notes redemption date																		August 2011
Percentage of redemption price									100.00%
Advances, variable-rate											2.08%		1.85%
Unamortized debt issuance costs related to notes									610,000	730,000				1,300,000	1,300,000
Junior subordinated deferrable interest debentures		123,712,000	123,712,000										123,700,000	123,700,000		123,700,000	12,400,000
Trust preferred securities, issued											120,000,000	120,000,000
Trust preferred securities, redeemed																	12,000,000
Maturity date of trust preferred securities											March 1, 2034
Common equity securities		$ 1,360,000	$ 11,240,000											$ 3,700,000
Maturity date								Feb. 15, 2017