Aggregate dividends declared during the period for each share of common stock outstanding.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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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Date the dividend to be paid was declared, in CCYY-MM-DD format.

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

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Shareholders' Equity - Summary of Common Stock Dividends and Distributions (Detail) - $ / shares								6 Months Ended
	Jul. 24, 2018	Apr. 24, 2018	Feb. 20, 2018	Oct. 24, 2017	Jul. 25, 2017	Apr. 25, 2017	Feb. 28, 2017	Jun. 30, 2018	Jun. 30, 2017
Dividends Payable [Line Items]
Dividends per Class A and Class C Common Share								$ 0.50	$ 0.50
Class A and Class C Common Share [Member]
Dividends Payable [Line Items]
Declaration Date		Apr. 24, 2018	Feb. 20, 2018	Oct. 24, 2017	Jul. 25, 2017	Apr. 25, 2017	Feb. 28, 2017
Record Date		Jun. 29, 2018	Mar. 30, 2018	Dec. 29, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017
Payment Date		Jul. 12, 2018	Apr. 12, 2018	Jan. 11, 2018	Oct. 12, 2017	Jul. 13, 2017	Apr. 13, 2017
Dividends per Class A and Class C Common Share		$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25
Subsequent Event [Member] \| Class A and Class C Common Share [Member]
Dividends Payable [Line Items]
Declaration Date	Jul. 24, 2018
Record Date	Sep. 28, 2018
Payment Date	Oct. 11, 2018
Dividends per Class A and Class C Common Share	$ 0.25