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Loans and Related Allowance of Loan and Lease Losses - Allowance for Loan Losses (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2016 | Dec. 31, 2015 | Sep. 30, 2015 | Mar. 31, 2015 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Sep. 30, 2016 | Sep. 30, 2015 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Individually evaluated for impairment |  |  |  |  |  |  |  |  |  |  |  |  | $ 544 | $ 833 | $ 1,596
Collectively evaluated for impairment |  |  |  |  |  |  |  |  |  |  |  |  | 5,790 | 5,552 | 5,250
Total ending allowance balance | $ 6,366 | $ 6,385 | $ 6,346 | $ 6,846 |  |  | $ 7,046 | $ 6,385 | $ 6,846 | $ 6,846 | $ 7,046 | $ 7,779 | 6,334 | 6,385 | 6,846
ALLL balance, period start | 6,366 | 6,320 | 6,346 | 6,846 |  |  | 7,046 | 6,385 | 6,846 | 6,846 | 7,046 | 7,779 |  |  |
Charge-offs | (226) |  | (229) |  |  |  |  | (679) | (1,109) | (1,197) | (1,212) | (1,330) |  |  |
Recoveries | 89 |  | 98 |  |  |  |  | 313 | 373 | 421 | 642 | 401 |  |  |
Provision | 105 | 105 | 105 | 105 | $ 70 | $ 120 | 180 | 315 | 210 | 315 | 370 | 196 |  |  |
ALLL balance, period end | 6,334 | 6,385 | 6,320 |  |  |  |  | 6,334 | 6,320 | 6,385 | 6,846 | 7,046 |  |  |
Commercial And Industrial [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Individually evaluated for impairment |  |  |  |  |  |  |  |  |  |  |  |  | 184 | 388 | 83
Collectively evaluated for impairment |  |  |  |  |  |  |  |  |  |  |  |  | 329 | 479 | 559
Total ending allowance balance | 484 | 867 | 610 | 642 |  |  | 614 | 867 | 642 | 642 | 614 | 1,732 | 513 | 867 | 642
ALLL balance, period start | 484 | 578 | 610 | 642 |  |  | 614 | 867 | 642 | 642 | 614 | 1,732 |  |  |
Charge-offs | (74) |  | (100) |  |  |  |  | (197) | (196) | (280) | (237) | (419) |  |  |
Recoveries | 4 |  | 5 |  |  |  |  | 51 | 186 | 207 | 121 | 191 |  |  |
Provision | 99 |  | 63 |  |  |  |  | (208) | (54) | 298 | 144 | (890) |  |  |
ALLL balance, period end | 513 | 867 | 578 |  |  |  |  | 513 | 578 | 867 | 642 | 614 |  |  |
Real Estate Construction Porfolio Segment [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Individually evaluated for impairment |  |  |  |  |  |  |  |  |  |  |  |  | 17 | 130 | 589
Collectively evaluated for impairment |  |  |  |  |  |  |  |  |  |  |  |  | 121 | 146 | 279
Total ending allowance balance | 159 | 276 | 363 | 868 |  |  | 576 | 276 | 868 | 868 | 576 | 1,123 | 138 | 276 | 868
ALLL balance, period start | 159 | 334 | 363 | 868 |  |  | 576 | 276 | 868 | 868 | 576 | 1,123 |  |  |
Charge-offs |  |  |  |  |  |  |  |  | (385) | (385) |  | (191) |  |  |
Recoveries |  |  |  |  |  |  |  |  |  |  | 60 | 33 |  |  |
Provision | (21) |  | (29) |  |  |  |  | (138) | (149) | (207) | 232 | (389) |  |  |
ALLL balance, period end | 138 | 276 | 334 |  |  |  |  | 138 | 334 | 276 | 868 | 576 |  |  |
Real Estate Mortgage Portfolio Segment [Member] | Residential Loan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Individually evaluated for impairment |  |  |  |  |  |  |  |  |  |  |  |  | 104 | 276 | 892
Collectively evaluated for impairment |  |  |  |  |  |  |  |  |  |  |  |  | 2,657 | 2,863 | 2,811
Total ending allowance balance | 2,788 | 3,139 | 3,347 | 3,703 |  |  | 3,664 | 3,139 | 3,703 | 3,703 | 3,664 | 2,872 | 2,761 | 3,139 | 3,703
ALLL balance, period start | 2,788 | 3,426 | 3,347 | 3,703 |  |  | 3,664 | 3,139 | 3,703 | 3,703 | 3,664 | 2,872 |  |  |
Charge-offs | (149) |  | (124) |  |  |  |  | (394) | (425) | (425) | (671) | (675) |  |  |
Recoveries | 82 |  | 81 |  |  |  |  | 113 | 161 | 186 | 267 | 107 |  |  |
Provision | 40 |  | 122 |  |  |  |  | (97) | (13) | (325) | 443 | 1,360 |  |  |
ALLL balance, period end | 2,761 | 3,139 | 3,426 |  |  |  |  | 2,761 | 3,426 | 3,139 | 3,703 | 3,664 |  |  |
Real Estate Mortgage Portfolio Segment [Member] | Commercial Loans [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Individually evaluated for impairment |  |  |  |  |  |  |  |  |  |  |  |  | 239 | 39 | 30
Collectively evaluated for impairment |  |  |  |  |  |  |  |  |  |  |  |  | 2,656 | 2,039 | 1,546
Total ending allowance balance | 2,909 | 2,078 | 1,978 | 1,576 |  |  | 2,170 | 2,078 | 1,576 | 1,576 | 2,170 | 1,991 | 2,895 | 2,078 | 1,576
ALLL balance, period start | 2,909 | 1,939 | 1,978 | 1,576 |  |  | 2,170 | 2,078 | 1,576 | 1,576 | 2,170 | 1,991 |  |  |
Charge-offs |  |  | (5) |  |  |  |  | (70) | (92) | (92) | (260) |  |  |  |
Recoveries |  |  | 5 |  |  |  |  | 140 | 5 | 5 | 40 | 46 |  |  |
Provision | (14) |  | (39) |  |  |  |  | 747 | 450 | 589 | (374) | 133 |  |  |
ALLL balance, period end | 2,895 | 2,078 | 1,939 |  |  |  |  | 2,895 | 1,939 | 2,078 | 1,576 | 2,170 |  |  |
Consumer Portfolio Segment [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Individually evaluated for impairment |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2
Collectively evaluated for impairment |  |  |  |  |  |  |  |  |  |  |  |  | 27 | 25 | 55
Total ending allowance balance | 26 | 25 | 48 | 57 |  |  | 22 | 25 | 57 | 57 | 22 | 61 | $ 27 | $ 25 | $ 57
ALLL balance, period start | 26 | 43 | 48 | $ 57 |  |  | $ 22 | 25 | 57 | 57 | 22 | 61 |  |  |
Charge-offs | (3) |  |  |  |  |  |  | (18) | (11) | (15) | (44) | (45) |  |  |
Recoveries | 3 |  | 7 |  |  |  |  | 9 | 21 | 23 | 154 | 24 |  |  |
Provision | 1 |  | (12) |  |  |  |  | 11 | (24) | (40) | (75) | (18) |  |  |
ALLL balance, period end | $ 27 | $ 25 | $ 43 |  |  |  |  | $ 27 | $ 43 | $ 25 | $ 57 | $ 22 |  |  |

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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=66008989&loc=SL6953423-111524 + 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=66008989&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 valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment. + 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=66008989&loc=SL6953423-111524 + 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=66008989&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=66008989&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=6379141&loc=d3e15032-111544 + Details
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