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Allowance for Loan Losses and Credit Quality of Loans, Changes in Allowance for Loan Losses (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Changes in allowance for loan losses by portfolio segment [Roll Forward] |  |  |
Balance, beginning of period | $ 65,200 | $ 63,018 | $ 66,359
Charge-offs | (33,087) | (29,299) | (26,087)
Recoveries | 6,399 | 6,050 | 4,461
Provision | 30,988 | 25,431 | 18,285
Balance, end of period | 69,500 | 65,200 | 63,018
Commercial Loans [Member] |  |  |
Changes in allowance for loan losses by portfolio segment [Roll Forward] |  |  |
Balance, beginning of period | 25,444 | 25,545 | 32,433
Charge-offs | (4,169) | (4,592) | (5,718)
Recoveries | 1,077 | 1,887 | 1,014
Provision | 5,254 | 2,604 | (2,184)
Balance, end of period | 27,606 | 25,444 | 25,545
Consumer Loans [Member] |  |  |
Changes in allowance for loan losses by portfolio segment [Roll Forward] |  |  |
Balance, beginning of period | 33,375 | 29,253 | 26,720
Charge-offs | (27,072) | (23,364) | (18,140)
Recoveries | 5,142 | 3,870 | 3,127
Provision | 25,385 | 23,616 | 17,546
Balance, end of period | 36,830 | 33,375 | 29,253
Residential Real Estate Mortgages [Member] |  |  |
Changes in allowance for loan losses by portfolio segment [Roll Forward] |  |  |
Balance, beginning of period | 6,381 | 7,960 | 7,130
Charge-offs | (1,846) | (1,343) | (2,229)
Recoveries | 180 | 293 | 320
Provision | 349 | (529) | 2,739
Balance, end of period | 5,064 | 6,381 | 7,960
Unallocated [Member] |  |  |
Changes in allowance for loan losses by portfolio segment [Roll Forward] |  |  |
Balance, beginning of period | 0 | 260 | 76
Charge-offs | 0 | 0 | 0
Recoveries | 0 | 0 | 0
Provision | 0 | (260) | 184
Balance, end of period | 0 | 0 | 260
Acquired Loans [Member] |  |  |
Changes in allowance for loan losses by portfolio segment [Roll Forward] |  |  |
Balance, beginning of period | 700 |  |
Charge-offs | (700) | (500) | $ (2,700)
Balance, end of period | $ 0 | $ 700 |

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- Definition Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts. + 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 (c)(4) -URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524 + Details
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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. + References No definition available. + Details
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- Definition Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss. + 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 (c)(3) -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 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 + Details
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- Definition 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 + Details
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