Debt - Summary of Notes Payable (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Unsecured Note [Member]
Debt Instrument [Line Items]
Discount and deferred financing charges, net of amortization	$ 0	$ 55
Notes Payable to Affiliates [Member]
Debt Instrument [Line Items]
Discount and deferred financing charges, net of amortization	$ 800	$ 2,000

Amount, after accumulated amortization, of debt discount (premium).

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Name:	us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant