Convertible Notes, Net - Summary of Outstanding Convertible Senior Notes (Parenthetical) (Detail)	12 Months Ended
Dec. 31, 2018 $ / shares	Dec. 31, 2017 USD ($) $ / shares
5.25% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price	$ 31.86
5.25% 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		$ 0
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
Debt instrument, conversion price		$ 0
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
Debt instrument, conversion price	$ 0
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
Debt instrument, conversion price		$ 0

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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The price per share of the conversion feature embedded in the debt instrument.

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Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

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