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

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

Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2018	Sep. 30, 2018	Sep. 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