Allowance for Probable Loan Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Allowance for probable loan losses
Balance at the beginning of the period	$ 65,051	$ 70,378	$ 58,193	$ 84,192
Losses charged to allowance	(3,845)	(4,036)	(10,410)	(31,789)
Recoveries credited to allowance	823	990	2,485	3,537
Net losses charged to allowance	(3,022)	(3,046)	(7,925)	(28,252)
Provision (credit) charged to operations	5,800	5,349	17,561	16,741
Balance at the end of the period	67,829	72,681	67,829	72,681
Commercial
Allowance for probable loan losses
Balance at the beginning of the period	20,676	24,688	11,632	26,617
Losses charged to allowance	(3,540)	(3,521)	(8,866)	(10,009)
Recoveries credited to allowance	658	821	1,909	2,823
Net losses charged to allowance	(2,882)	(2,700)	(6,957)	(7,186)
Provision (credit) charged to operations	3,370	3,312	16,489	5,869
Balance at the end of the period	21,164	25,300	21,164	25,300
Commercial real estate: other construction and land development
Allowance for probable loan losses
Balance at the beginning of the period	11,624	13,242	12,720	19,940
Losses charged to allowance	(2)	(3)	(250)	(7,574)
Recoveries credited to allowance	10	13	36	225
Net losses charged to allowance	8	10	(214)	(7,349)
Provision (credit) charged to operations	(10)	44	(884)	705
Balance at the end of the period	11,622	13,296	11,622	13,296
Commercial real estate: farmland and commercial
Allowance for probable loan losses
Balance at the beginning of the period	22,383	20,551	21,880	24,227
Losses charged to allowance		(1)	(61)	(12,477)
Recoveries credited to allowance	9	32	150	163
Net losses charged to allowance	9	31	89	(12,314)
Provision (credit) charged to operations	1,549	1,138	1,972	9,807
Balance at the end of the period	23,941	21,720	23,941	21,720
Commercial real estate: multifamily
Allowance for probable loan losses
Balance at the beginning of the period	623	803	694	1,003
Provision (credit) charged to operations	112	(27)	41	(227)
Balance at the end of the period	735	776	735	776
Residential: first lien
Allowance for probable loan losses
Balance at the beginning of the period	3,855	3,987	4,390	4,562
Losses charged to allowance	(22)	(63)	(221)	(129)
Recoveries credited to allowance	45	4	54	7
Net losses charged to allowance	23	(59)	(167)	(122)
Provision (credit) charged to operations	186	272	(159)	(240)
Balance at the end of the period	4,064	4,200	4,064	4,200
Residential: junior lien
Allowance for probable loan losses
Balance at the beginning of the period	4,047	4,410	4,448	4,760
Losses charged to allowance	(149)	(282)	(544)	(993)
Recoveries credited to allowance	80	62	204	168
Net losses charged to allowance	(69)	(220)	(340)	(825)
Provision (credit) charged to operations	404	626	274	881
Balance at the end of the period	4,382	4,816	4,382	4,816
Consumer
Allowance for probable loan losses
Balance at the beginning of the period	797	1,476	1,289	1,724
Losses charged to allowance	(130)	(159)	(446)	(595)
Recoveries credited to allowance	21	58	127	151
Net losses charged to allowance	(109)	(101)	(319)	(444)
Provision (credit) charged to operations	124	31	(158)	126
Balance at the end of the period	812	1,406	812	1,406
Foreign
Allowance for probable loan losses
Balance at the beginning of the period	1,046	1,221	1,140	1,359
Losses charged to allowance	(2)	(7)	(22)	(12)
Recoveries credited to allowance			5
Net losses charged to allowance	(2)	(7)	(17)	(12)
Provision (credit) charged to operations	65	(47)	(14)	(180)
Balance at the end of the period	$ 1,109	$ 1,167	$ 1,109	$ 1,167