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Leases - Additional Information (Detail) | 1 Months Ended | 12 Months Ended
--- | --- | ---
Aug. 31, 2017 ft² yr | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Leases [Line Items] |  |  |  |
Rent expense |  | $ 4,700,000 | $ 3,200,000 | $ 3,200,000
Deferred rent |  | 6,000,000 | 6,600,000 |
Repayment of capital lease |  | 5,131,000 | $ 5,945,000 | $ 5,187,000
Capital lease balance |  | $ 0 |  |
ARE-San Francisco No. 19, LLC [Member] |  |  |  |
Leases [Line Items] |  |  |  |
Extended lease term start year | 2020 |  |  |
Lease expiration year | 2030 |  |  |
Lease space | ft² | 129,732 |  |  |
Lease description option to extend |  | The term of the Lease commenced on September 1, 2017, and will expire January 31, 2030, subject to our right to extend the term of the Lease for two consecutive five-year periods. |  |
Number of consecutive 5 year terms to extend lease | yr | 2 |  |  |
Lease extension term | 5 years |  |  |
Lease commencement date | Sep. 01, 2017 |  |  |
Lease expiration date | Jan. 31, 2030 |  |  |
Additional space required to be leased in the future | ft² | 23,000 |  |  |

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- Definition Number of consecutive five year terms to extend lease. + References No definition available. + Details
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- Definition Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84164817&loc=d3e45280-112737 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition For a classified balance sheet, the cumulative difference between the rental income or payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense, by the lessor or lessee, respectively, more than one year after the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.26(c)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 25 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77902458&loc=d3e39927-112707 + Details
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- Definition Description of terms and conditions of option to extend lessee's operating lease. Includes, but is not limited to, information about option recognized as part of right-of-use asset and lease liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980 + Details
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