Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Percentage of comparable consolidated amounts	95.00%	95.00%
ASU 2016-01 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Decrease in net income	$ 390
ASU 2016-01 [Member] \| Common Shares [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Decrease in diluted earnings per common share	$ 0.02

Amount of the effect of a change in accounting principle on diluted earnings per share.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1252-109256

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1278-109256

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22583-107794

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22580-107794

Name:	us-gaap_NewAccountingPronouncementOrChangeInAccountingPrincipleEffectOfChangeOnDilutedEarningsPerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration