Stockholders' Equity - Summary of Cash Dividends Declared on Class A Common Stock (Detail) - $ / shares	3 Months Ended
Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Equity [Abstract]
Dividends per share (in dollars per share)	$ 0.4220	$ 0.4220	$ 0.4220
Declaration Date	Aug. 02, 2018	May 03, 2018	Feb. 22, 2018
Record Date	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018
Payment Date	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018

Date the declared dividend will be paid, in CCYY-MM-DD format.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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The per share amount of a dividend declared, but not paid, as of the financial reporting date.

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Date the dividend to be paid was declared, in CCYY-MM-DD format.

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- Definition

Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

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