Convertible Debt (Details)						1 Months Ended	12 Months Ended
	Aug. 19, 2019 USD ($) day $ / shares	Aug. 14, 2019 $ / shares	Nov. 19, 2018 USD ($) day $ / shares	Sep. 15, 2017 USD ($) day $ / shares	Sep. 11, 2017 institution $ / shares	Nov. 30, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Number of Initial Purchasers | institution					2
Proceeds from issuance of convertible notes, net of issuance costs							$ 935,146,000	$ 562,047,000	$ 420,449,000
Premiums paid for capped call confirmations							145,728,000	93,438,000	$ 44,160,000
Convertible Debt | 2017 Notes
Debt Instrument [Line Items]
Principal				$ 431,250,000			431,250,000	431,250,000
Interest rate, stated percentage				0.375%
Proceeds from issuance of convertible notes, net of issuance costs				$ 420,400,000
Premiums paid for capped call confirmations				$ 44,200,000
Effective interest rate, percentage				6.00%
Equity component of Notes				$ 95,800,000
Fair value of Notes							469,500,000	465,000,000.0
Conversion ratio				0.00961
Conversion price (in usd per share) | $ / shares				$ 104.06
Trading days (whether or not consecutively) | day				20
Trading days (consecutive) | day				30
Percentage of conversion stock price				130.00%
During number of business day period				5 days
Consecutive trading day period (after any)				10 days
Principal amount of Notes				$ 1,000
Measurement period percentage (less than)				98.00%
Minimum number of trading days immediately preceding the date on which notice or redemption provided | day				1
Trading days immediately preceding date on which notice of redemption provided | day				5
Redemption price, percentage of principal amount to be redeemed				100.00%
Default percentage of aggregate principal amount, of notes outstanding (not less than)				25.00%
Convertible Debt | 2017 Notes | Class A common stock
Debt Instrument [Line Items]
Conversion price (in usd per share) | $ / shares				$ 104.06
Cap price per share (in usd per share) | $ / shares					$ 154.16
Premium over last reported sale price, percentage					100.00%
Convertible Debt | 2017 Notes | Over-Allotment Option
Debt Instrument [Line Items]
Over-allotment option included in issuance of notes				$ 56,250,000
Convertible Debt | 2018 Notes
Debt Instrument [Line Items]
Principal			$ 500,000,000.0			$ 575,000,000.0	575,000,000	575,000,000
Interest rate, stated percentage						1.125%
Over-allotment option included in issuance of notes			$ 75,000,000.0			$ 75,000,000.0
Proceeds from issuance of convertible notes, net of issuance costs						562,000,000.0
Premiums paid for capped call confirmations						$ 93,400,000
Effective interest rate, percentage						8.10%
Equity component of Notes						$ 181,500,000
Fair value of Notes							597,000,000.0	$ 580,200,000
Conversion ratio			0.008591
Trading days (whether or not consecutively) | day			20
Trading days (consecutive) | day			30
Percentage of conversion stock price			130.00%
During number of business day period			5 years
Consecutive trading day period (after any)			10 years
Principal amount of Notes			$ 1,000
Measurement period percentage (less than)			98.00%
Redemption price, percentage of principal amount to be redeemed			100.00%
Default percentage of aggregate principal amount, of notes outstanding (not less than)			25.00%
Convertible Debt | 2018 Notes | Class A common stock
Debt Instrument [Line Items]
Interest rate, stated percentage			1.125%
Conversion price (in usd per share) | $ / shares			$ 116.40
Cap price per share (in usd per share) | $ / shares			$ 219.63
Premium over last reported sale price, percentage			150.00%
Convertible Debt | 2019 Notes
Debt Instrument [Line Items]
Principal	$ 948,750,000						948,750,000
Interest rate, stated percentage	1.00%
Over-allotment option included in issuance of notes	$ 123,750,000
Proceeds from issuance of convertible notes, net of issuance costs	935,100,000
Premiums paid for capped call confirmations	$ 145,700,000
Effective interest rate, percentage	6.40%
Equity component of Notes	$ 280,300,000
Fair value of Notes							$ 834,000,000.0
Conversion ratio	0.0067349
Trading days (consecutive) | day	30
Percentage of conversion stock price	130.00%
During number of business day period	5 years
Consecutive trading day period (after any)	10 years
Principal amount of Notes	$ 1,000
Measurement period percentage (less than)	98.00%
Redemption price, percentage of principal amount to be redeemed	100.00%
Default percentage of aggregate principal amount, of notes outstanding (not less than)	25.00%
Convertible Debt | 2019 Notes | Class A common stock
Debt Instrument [Line Items]
Interest rate, stated percentage	1.00%
Conversion price (in usd per share) | $ / shares	$ 148.48
Trading days (whether or not consecutively) | day	20
Trading days (consecutive) | day	30
Cap price per share (in usd per share) | $ / shares	$ 280.15	$ 280.15
Premium over last reported sale price, percentage		150.00%