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Fair Value Measurements - Additional Information (Detail) - USD ($) | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2019 | Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Lease payment liability | $ 55,851,000 |
Transfers of assets from level 1 to 2 | 0 | $ 0
Transfers of assets from level 2 to 1 | 0 | 0
Transfers of liabilities from level 1 to 2 | 0 | 0
Transfers of liabilities from level 2 to 1 | 0 | 0
Transfers of assets into level 3 | 0 | 0
Transfers of assets out of level 3 | 0 | 0
Transfers of liabilities into level 3 | 0 | 0
Transfers of liabilities out of level 3 | $ 0 | 0
Shorenstein Properties LLC [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Lease commencement date | 2008 |
Lease payment liability | $ 5,000,000.0 |
Remaining lease term | 2023 |
Building [Member] | Shorenstein Properties LLC [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Lease maximum expansion period | 31 months |
Lease obligations [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Liabilities fair value disclosure | $ 1,745,000 | 98,105,000
Lease obligations [Member] | Long-term property lease [Member] | Shorenstein Properties LLC [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Liabilities fair value disclosure | $ 1,700,000 |
Lease obligations [Member] | Building [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Liabilities fair value disclosure |  | $ 96,200,000

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