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Leases - Additional Information (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2019 | Apr. 01, 2018
Lessee, Lease, Description [Line Items] |  |
Payments expected to be made on leases not yet commenced | $ 1,789 |
Rent expense under operating leases |  | $ 18,901
Minimum |  |
Lessee, Lease, Description [Line Items] |  |
Lease renewal terms | 1 year |
Contract terms for leases not yet commenced | 3 years |
Maximum |  |
Lessee, Lease, Description [Line Items] |  |
Lease renewal terms | 50 years |
Contract terms for leases not yet commenced | 6 years 4 months 24 days |

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- Definition Lessee, Lease Not Yet Commenced, Liability + References No definition available. + Details
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Namespace Prefix: | son_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Lessee, Lease, Renewal Term + References No definition available. + Details
Name: | son_LesseeLeaseRenewalTerm
Namespace Prefix: | son_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_LesseeLeaseDescriptionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Term of lessee's operating lease not yet commenced, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | instant

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- Definition Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41499-112717 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
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