Allowance for Probable Loan Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Allowance for probable loan losses
Balance at the beginning of the period	$ 70,161	$ 58,193
Losses charged to allowance	(2,844)	(3,509)
Recoveries credited to allowance	1,013	865
Net losses charged to allowance	(1,831)	(2,644)
Provision charged to operations	2,078	7,419
Balance at the end of the period	70,408	62,968
Commercial
Allowance for probable loan losses
Balance at the beginning of the period	22,433	11,632
Losses charged to allowance	(2,481)	(2,663)
Recoveries credited to allowance	796	694
Net losses charged to allowance	(1,685)	(1,969)
Provision charged to operations	7,175	11,263
Balance at the end of the period	27,923	20,926
Commercial real estate: other construction and land development
Allowance for probable loan losses
Balance at the beginning of the period	12,541	12,720
Losses charged to allowance		(128)
Recoveries credited to allowance	31	13
Net losses charged to allowance	31	(115)
Provision charged to operations	903	(1,552)
Balance at the end of the period	13,475	11,053
Commercial real estate: farmland and commercial
Allowance for probable loan losses
Balance at the beginning of the period	24,467	21,880
Losses charged to allowance		(60)
Recoveries credited to allowance	23	13
Net losses charged to allowance	23	(47)
Provision charged to operations	(5,556)	(1,182)
Balance at the end of the period	18,934	20,651
Commercial real estate: multifamily
Allowance for probable loan losses
Balance at the beginning of the period	776	694
Provision charged to operations	43	(85)
Balance at the end of the period	819	609
Residential: first lien
Allowance for probable loan losses
Balance at the beginning of the period	3,812	4,390
Losses charged to allowance	(27)	(172)
Recoveries credited to allowance	4	5
Net losses charged to allowance	(23)	(167)
Provision charged to operations	(265)	(355)
Balance at the end of the period	3,524	3,868
Residential: junior lien
Allowance for probable loan losses
Balance at the beginning of the period	4,249	4,448
Losses charged to allowance	(146)	(255)
Recoveries credited to allowance	33	94
Net losses charged to allowance	(113)	(161)
Provision charged to operations	(168)	(276)
Balance at the end of the period	3,968	4,011
Consumer
Allowance for probable loan losses
Balance at the beginning of the period	750	1,289
Losses charged to allowance	(187)	(211)
Recoveries credited to allowance	80	46
Net losses charged to allowance	(107)	(165)
Provision charged to operations	105	(304)
Balance at the end of the period	748	820
Foreign
Allowance for probable loan losses
Balance at the beginning of the period	1,133	1,140
Losses charged to allowance	(3)	(20)
Recoveries credited to allowance	46
Net losses charged to allowance	43	(20)
Provision charged to operations	(159)	(90)
Balance at the end of the period	$ 1,017	$ 1,030