Loans and Allowance - Changes in Allowance for Loan Losses by Loan Segment (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Allowance for loan losses:
Beginning balance	$ 75,032	$ 66,037
Provision for losses	2,500	2,385
Recoveries on loans	701	1,268
Loans charged off	(1,813)	(1,465)
Ending balance	76,420	68,225
Commercial
Allowance for loan losses:
Beginning balance	30,418	27,696
Provision for losses	840	1,197
Recoveries on loans	119	366
Loans charged off	(609)	(735)
Ending balance	30,768	28,524
Commercial Real Estate
Allowance for loan losses:
Beginning balance	27,343	23,661
Provision for losses	84	247
Recoveries on loans	339	564
Loans charged off	(61)	(152)
Ending balance	27,705	24,320
Consumer
Allowance for loan losses:
Beginning balance	3,732	2,923
Provision for losses	274	249
Recoveries on loans	89	101
Loans charged off	(199)	(153)
Ending balance	3,896	3,120
Residential
Allowance for loan losses:
Beginning balance	13,537	11,755
Provision for losses	1,302	692
Recoveries on loans	154	237
Loans charged off	(944)	(425)
Ending balance	14,049	12,259
Lease financing receivables, net of unearned income
Allowance for loan losses:
Beginning balance	2	2
Provision for losses
Recoveries on loans
Loans charged off
Ending balance	$ 2	$ 2

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

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- Definition

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 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

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Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

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