Earnings Per Share - Additional Information (Detail) - shares	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Line Items]
Options excluded from the computation of diluted earnings	190,364	126,636
Class A Common Stock [Member]
Earnings Per Share [Line Items]
Common stock, voting rights	One vote per share
Class B Common Stock [Member]
Earnings Per Share [Line Items]
Common stock, voting rights	Ten votes per share

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration