Loans and Allowance - Changes in Allowance for Loan Losses by Loan Segment (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Allowance for loan losses:
Beginning balance	$ 76,420	$ 68,225	$ 75,032	$ 66,037
Provision for losses	1,663	2,875	4,163	5,260
Recoveries on loans	3,190	726	3,891	1,994
Loans charged off	(3,730)	(1,355)	(5,543)	(2,820)
Ending balance	77,543	70,471	77,543	70,471
Commercial
Allowance for loan losses:
Beginning balance	30,768	28,524	30,418	27,696
Provision for losses	471	161	1,311	1,358
Recoveries on loans	1,283	297	1,402	663
Loans charged off	(1,057)	(76)	(1,666)	(811)
Ending balance	31,465	28,906	31,465	28,906
Commercial Real Estate
Allowance for loan losses:
Beginning balance	27,705	24,320	27,343	23,661
Provision for losses	954	1,402	1,038	1,649
Recoveries on loans	1,213	175	1,552	739
Loans charged off	(2,141)	(661)	(2,202)	(813)
Ending balance	27,731	25,236	27,731	25,236
Consumer
Allowance for loan losses:
Beginning balance	3,896	3,120	3,732	2,923
Provision for losses	60	286	334	535
Recoveries on loans	98	101	187	202
Loans charged off	(133)	(135)	(332)	(288)
Ending balance	3,921	3,372	3,921	3,372
Residential
Allowance for loan losses:
Beginning balance	14,049	12,259	13,537	11,755
Provision for losses	178	1,026	1,480	1,718
Recoveries on loans	596	153	750	390
Loans charged off	(399)	(483)	(1,343)	(908)
Ending balance	14,424	12,955	14,424	12,955
Lease financing receivables, net of unearned income
Allowance for loan losses:
Beginning balance	2	2	2	2
Provision for losses
Recoveries on loans
Loans charged off
Ending balance	$ 2	$ 2	$ 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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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
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-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
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-Section S99
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-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
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-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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