Allowance for Credit Losses (By Loan Class) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Allowance for probable loan losses
Balance at the beginning of the period	$ 60,278	$ 61,384
Losses charged to allowance	(2,980)	(2,835)
Recoveries credited to allowance	792	1,061
Net losses (recoveries) charged to allowance	(2,188)	(1,774)
Provision for credit loss expenses	16,836	7,420
Balance at the end of the period	85,273	67,030
Watch - List Impaired
Allowance for probable loan losses
Losses charged to allowance		(9,500)
Commercial
Allowance for probable loan losses
Balance at the beginning of the period	11,145	12,596
Losses charged to allowance	(2,819)	(2,764)
Recoveries credited to allowance	671	638
Net losses (recoveries) charged to allowance	(2,148)	(2,126)
Provision for credit loss expenses	5,823	942
Balance at the end of the period	19,067	11,412
Real estate - construction
Allowance for probable loan losses
Balance at the beginning of the period	18,152	15,123
Recoveries credited to allowance		20
Net losses (recoveries) charged to allowance		20
Provision for credit loss expenses	5,878	(354)
Balance at the end of the period	37,421	14,789
Commercial Real Estate: Farmland and Commercial
Allowance for probable loan losses
Balance at the beginning of the period	16,533	19,353
Losses charged to allowance	(55)	(1)
Recoveries credited to allowance	9	283
Net losses (recoveries) charged to allowance	(46)	282
Provision for credit loss expenses	2,809	6,245
Balance at the end of the period	15,004	25,880
Commercial Real Estate: Multifamily
Allowance for probable loan losses
Balance at the beginning of the period	1,786	1,808
Provision for credit loss expenses	327	537
Balance at the end of the period	1,758	2,345
Residential First Lien
Allowance for probable loan losses
Balance at the beginning of the period	3,762	3,467
Losses charged to allowance	(36)	(1)
Recoveries credited to allowance	1	1
Net losses (recoveries) charged to allowance	(35)
Provision for credit loss expenses	635	79
Balance at the end of the period	2,782	3,546
Residential Junior Lien
Allowance for probable loan losses
Balance at the beginning of the period	7,535	7,719
Losses charged to allowance		(6)
Recoveries credited to allowance	103	102
Net losses (recoveries) charged to allowance	103	96
Provision for credit loss expenses	1,243	(70)
Balance at the end of the period	8,452	7,745
Consumer
Allowance for probable loan losses
Balance at the beginning of the period	542	447
Losses charged to allowance	(70)	(63)
Recoveries credited to allowance	8	17
Net losses (recoveries) charged to allowance	(62)	(46)
Provision for credit loss expenses	68	61
Balance at the end of the period	323	462
Foreign
Allowance for probable loan losses
Balance at the beginning of the period	823	871
Provision for credit loss expenses	53	(20)
Balance at the end of the period	466	$ 851
ASU 2016-13 | Restatement Adjustment
Allowance for probable loan losses
Balance at the beginning of the period	10,347
ASU 2016-13 | Commercial | Restatement Adjustment
Allowance for probable loan losses
Balance at the beginning of the period	4,247
ASU 2016-13 | Real estate - construction | Restatement Adjustment
Allowance for probable loan losses
Balance at the beginning of the period	13,391
ASU 2016-13 | Commercial Real Estate: Farmland and Commercial | Restatement Adjustment
Allowance for probable loan losses
Balance at the beginning of the period	(4,292)
ASU 2016-13 | Commercial Real Estate: Multifamily | Restatement Adjustment
Allowance for probable loan losses
Balance at the beginning of the period	(355)
ASU 2016-13 | Residential First Lien | Restatement Adjustment
Allowance for probable loan losses
Balance at the beginning of the period	(1,580)
ASU 2016-13 | Residential Junior Lien | Restatement Adjustment
Allowance for probable loan losses
Balance at the beginning of the period	(429)
ASU 2016-13 | Consumer | Restatement Adjustment
Allowance for probable loan losses
Balance at the beginning of the period	(225)
ASU 2016-13 | Foreign | Restatement Adjustment
Allowance for probable loan losses
Balance at the beginning of the period	$ (410)