Allowance for Probable Loan Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Allowance for probable loan losses
Balance at the beginning of the period	$ 78,781	$ 85,397	$ 84,192	$ 84,482
Losses charged to allowance	(15,669)	(6,021)	(27,753)	(10,490)
Recoveries credited to allowance	1,159	1,022	2,547	2,326
Net losses charged to allowance	(14,510)	(4,999)	(25,206)	(8,164)
(Credit) provision charged to operations	6,107	(1,917)	11,392	2,163
Balance at the end of the period	70,378	78,481	70,378	78,481
Commercial
Allowance for probable loan losses
Balance at the beginning of the period	24,577	21,793	26,617	22,046
Losses charged to allowance	(3,064)	(3,865)	(6,488)	(6,819)
Recoveries credited to allowance	758	771	2,002	1,671
Net losses charged to allowance	(2,306)	(3,094)	(4,486)	(5,148)
(Credit) provision charged to operations	2,417	1,928	2,557	3,729
Balance at the end of the period	24,688	20,627	24,688	20,627
Commercial real estate: other construction and land development
Allowance for probable loan losses
Balance at the beginning of the period	19,766	31,471	19,940	26,695
Losses charged to allowance	(7,500)	(277)	(7,571)	(1,218)
Recoveries credited to allowance	207	71	212	74
Net losses charged to allowance	(7,293)	(206)	(7,359)	(1,144)
(Credit) provision charged to operations	769	(11,189)	661	(5,475)
Balance at the end of the period	13,242	20,076	13,242	20,076
Commercial real estate: farmland and commercial
Allowance for probable loan losses
Balance at the beginning of the period	21,810	18,562	24,227	16,340
Losses charged to allowance	(4,482)	(645)	(12,476)	(645)
Recoveries credited to allowance	100	60	131	194
Net losses charged to allowance	(4,382)	(585)	(12,345)	(451)
(Credit) provision charged to operations	3,123	3,351	8,669	5,439
Balance at the end of the period	20,551	21,328	20,551	21,328
Commercial real estate: multifamily
Allowance for probable loan losses
Balance at the beginning of the period	849	231	1,003	53
(Credit) provision charged to operations	(46)	623	(200)	801
Balance at the end of the period	803	854	803	854
Residential: first lien
Allowance for probable loan losses
Balance at the beginning of the period	4,379	4,441	4,562	10,059
Losses charged to allowance	(30)	(638)	(66)	(659)
Recoveries credited to allowance	1	2	3	4
Net losses charged to allowance	(29)	(636)	(63)	(655)
(Credit) provision charged to operations	(363)	2,305	(512)	(3,294)
Balance at the end of the period	3,987	6,110	3,987	6,110
Residential: junior lien
Allowance for probable loan losses
Balance at the beginning of the period	4,505	4,273	4,760	2,611
Losses charged to allowance	(399)	(331)	(711)	(566)
Recoveries credited to allowance	61	67	106	264
Net losses charged to allowance	(338)	(264)	(605)	(302)
(Credit) provision charged to operations	243	1,524	255	3,224
Balance at the end of the period	4,410	5,533	4,410	5,533
Consumer
Allowance for probable loan losses
Balance at the beginning of the period	1,602	4,058	1,724	6,241
Losses charged to allowance	(189)	(261)	(436)	(570)
Recoveries credited to allowance	32	50	93	118
Net losses charged to allowance	(157)	(211)	(343)	(452)
(Credit) provision charged to operations	31	(1,469)	95	(3,411)
Balance at the end of the period	1,476	2,378	1,476	2,378
Foreign
Allowance for probable loan losses
Balance at the beginning of the period	1,293	568	1,359	437
Losses charged to allowance	(5)	(4)	(5)	(13)
Recoveries credited to allowance		1		1
Net losses charged to allowance	(5)	(3)	(5)	(12)
(Credit) provision charged to operations	(67)	1,010	(133)	1,150
Balance at the end of the period	$ 1,221	$ 1,575	$ 1,221	$ 1,575