The amount of the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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Convertible Notes, Net - Summary of Outstanding Convertible Senior Notes (Parenthetical) (Detail)				9 Months Ended
	Oct. 15, 2018	Jul. 16, 2018	Mar. 28, 2018 USD ($) $ / shares	Sep. 30, 2018 USD ($) $ / shares	Sep. 28, 2018 $ / shares
5.25% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price					$ 33.51
Convertible Notes, debt conversion, common stock issued, in percent				36.5472
5.25% Convertible Senior Notes [Member] \| Class A Common Stock [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, principal amount \| $				$ 1,000
4.38% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, common stock issued, in percent				28.0324
4.38% Convertible Senior Notes [Member] \| Class A Common Stock [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, principal amount \| $				$ 1,000
Convertible Senior Notes [Member] \| Class A Common Stock [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, principal amount \| $			$ 1,000
Debt instrument, conversion price			$ 27.67
Convertible Notes, debt conversion, common stock issued, in percent		36.8161	36.1380
Convertible Senior Notes [Member] \| Class A Common Stock [Member] \| Subsequent Events [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, common stock issued, in percent	36.8161
5.25% Convertible Senior Notes Issued in November 2013 [Member] \| Class A Common Stock [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price				$ 27.36
4.38% Convertible Senior Notes Issued in May 2017 [Member] \| Class A Common Stock [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price				$ 35.67
4.75% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, common stock issued, in percent				27.6052
4.75% Convertible Senior Notes [Member] \| Class A Common Stock [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, principal amount \| $				$ 1,000
4.75% Convertible Senior Notes Issued In March 2018 [Member] \| Class A Common Stock [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price				$ 36.23