v3.8.0.1

Summary of Significant Accounting Policies - Balances of Financial Instruments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Interest rate swap, assets | $ 11,008 | $ 9,598
Interest rate swap, liabilities | (5,020) | (10,217)
Fair Value, Measurements, Recurring |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Interest rate swap, assets | 11,008 | 9,598
Interest rate swap, liabilities | (5,020) | (10,217)
Interest rate derivatives, at fair value, net | 5,988 | (619)
Fair Value, Measurements, Recurring | Level 2 |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Interest rate swap, assets | 11,008 | 9,598
Interest rate swap, liabilities | (5,020) | (10,217)
Interest rate derivatives, at fair value, net | $ 5,988 | $ (619)

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