Earnings Per Share - Additional Information (Detail) - shares	Jun. 30, 2018	Dec. 31, 2017
Participating Restricted Shares and Share Units [Member]
Earning Per Share [Line Items]
Unvested restricted stock outstanding	139,000	67,000
Time Based Restricted Shares and Share Units [Member]
Earning Per Share [Line Items]
Unvested restricted stock outstanding	490,450	245,570

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant