Long-Term Debt - Tremont Promissory Note Payable - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
Jan. 31, 2018	Mar. 31, 2018
Promissory Note \| Tremont
Debt Instrument [Line Items]
Principal prepayments of note	$ 2.2	$ 2.2

The cash outflow for a borrowing supported by a written promise to pay an obligation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3291-108585

Name:	us-gaap_RepaymentsOfNotesPayable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration