Fair Value of Financial Instruments - Carrying Amounts and Fair Values of Financial Instruments Measured based on Level Two Inputs (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Carrying Value
Fair Value of Financial Instruments
Indebtedness	$ 580,446	$ 517,272
Interest rate liabilities	136	69
Interest rate assets	2,860	1,525
Fair Value \| Level 2
Fair Value of Financial Instruments
Indebtedness	576,270	518,417
Interest rate liabilities	136	69
Interest rate assets	$ 2,860	$ 1,525

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

No definition available.

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant