Loans and Allowance - Changes in Allowance for Loan Losses by Loan Segment (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Allowance for loan losses:
Beginning balance	$ 77,543	$ 70,471	$ 75,032	$ 66,037
Provision for losses	1,400	2,083	5,563	7,343
Recoveries on loans	1,175	1,859	5,066	3,853
Loans charged off	(1,712)	(1,059)	(7,255)	(3,879)
Ending balance	78,406	73,354	78,406	73,354
Commercial
Allowance for loan losses:
Beginning balance	31,465	28,906	30,418	27,696
Provision for losses	256	921	1,567	2,279
Recoveries on loans	658	324	2,060	987
Loans charged off	(313)	(468)	(1,979)	(1,279)
Ending balance	32,066	29,683	32,066	29,683
Commercial Real Estate
Allowance for loan losses:
Beginning balance	27,731	25,236	27,343	23,661
Provision for losses	410	374	1,448	2,023
Recoveries on loans	306	1,327	1,858	2,066
Loans charged off	(501)	(190)	(2,703)	(1,003)
Ending balance	27,946	26,747	27,946	26,747
Consumer
Allowance for loan losses:
Beginning balance	3,921	3,372	3,732	2,923
Provision for losses	159	342	493	877
Recoveries on loans	46	51	233	253
Loans charged off	(194)	(174)	(526)	(462)
Ending balance	3,932	3,591	3,932	3,591
Residential
Allowance for loan losses:
Beginning balance	14,424	12,955	13,537	11,755
Provision for losses	575	446	2,055	2,164
Recoveries on loans	165	157	915	547
Loans charged off	(704)	(227)	(2,047)	(1,135)
Ending balance	14,460	13,331	14,460	13,331
Finance Leases
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.

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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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