Allowance for Probable Loan Losses (By Loan Class) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Allowance for probable loan losses
Balance at the beginning of the period	$ 61,384	$ 67,687
Losses charged to allowance	(2,835)	(2,877)
Recoveries credited to allowance	1,061	682
Net losses (recoveries) charged to allowance	(1,774)	(2,195)
Provision charged to operations	7,420	1,662
Balance at the end of the period	$ 67,030	67,154
Period of time for determining the historical charge-off experience	3 years
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	12,596	27,905
Losses charged to allowance	(2,764)	(2,715)
Recoveries credited to allowance	638	583
Net losses (recoveries) charged to allowance	(2,126)	(2,132)
Provision charged to operations	942	(5,082)
Balance at the end of the period	11,412	20,691
Commercial Real Estate:Other Construction and Land Development
Allowance for probable loan losses
Balance at the beginning of the period	15,123	11,675
Losses charged to allowance		(1)
Recoveries credited to allowance	20	2
Net losses (recoveries) charged to allowance	20	1
Provision charged to operations	(354)	122
Balance at the end of the period	14,789	11,798
Commercial Real Estate: Farmland and Commercial
Allowance for probable loan losses
Balance at the beginning of the period	19,353	16,663
Losses charged to allowance	(1)
Recoveries credited to allowance	283	18
Net losses (recoveries) charged to allowance	282	18
Provision charged to operations	6,245	8,122
Balance at the end of the period	25,880	24,803
Commercial Real Estate: Multifamily
Allowance for probable loan losses
Balance at the beginning of the period	1,808	1,109
Provision charged to operations	537	(162)
Balance at the end of the period	2,345	947
Residential First Lien
Allowance for probable loan losses
Balance at the beginning of the period	3,467	2,950
Losses charged to allowance	(1)	(14)
Recoveries credited to allowance	1	1
Net losses (recoveries) charged to allowance		(13)
Provision charged to operations	79	69
Balance at the end of the period	3,546	3,006
Residential Junior Lien
Allowance for probable loan losses
Balance at the beginning of the period	7,719	6,103
Losses charged to allowance	(6)	(30)
Recoveries credited to allowance	102	66
Net losses (recoveries) charged to allowance	96	36
Provision charged to operations	(70)	(1,450)
Balance at the end of the period	7,745	4,689
Consumer
Allowance for probable loan losses
Balance at the beginning of the period	447	440
Losses charged to allowance	(63)	(117)
Recoveries credited to allowance	17	12
Net losses (recoveries) charged to allowance	(46)	(105)
Provision charged to operations	61	102
Balance at the end of the period	462	437
Foreign
Allowance for probable loan losses
Balance at the beginning of the period	871	842
Provision charged to operations	(20)	(59)
Balance at the end of the period	$ 851	$ 783

Period of time that is used to determine the historical charge-off experience.

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Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount, after recoveries, of loans and leases that have been written-off.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount of expense related to estimated loss from loan and lease transactions.

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