Convertible Senior Notes and Capped Call Transactions - Narrative (Details) $ / shares in Units, shares in Thousands	1 Months Ended		12 Months Ended
	Dec. 31, 2020 USD ($) equity_instrument day $ / shares shares	Mar. 31, 2019 USD ($) equity_instrument day $ / shares shares	Dec. 31, 2020 USD ($) $ / shares	Dec. 31, 2019 USD ($) $ / shares
Debt Instrument [Line Items]
Common stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001	$ 0.001	$ 0.001
Adjustments to additional paid in capital related to issuance costs attributable to equity component			$ 3,797,000	$ 1,986,000
Number of shares of common stock covered by called caps (shares) | shares	6,880	5,960
Reduction to additional paid-in-capital related to called caps	$ 46,100,000	$ 23,200,000	46,058,000	$ 23,184,000
2024 Notes
Debt Instrument [Line Items]
Carry amount of equity component of convertible notes		52,900,000
Total deferred issuance costs		8,600,000
Debt issuance costs attributable to liability		6,600,000
Adjustments to additional paid in capital related to issuance costs attributable to equity component		$ 2,000,000.0
2026 Notes
Debt Instrument [Line Items]
Carry amount of equity component of convertible notes	162,500,000		162,500,000
Total deferred issuance costs	12,200,000		12,200,000
Debt issuance costs attributable to liability	8,500,000		$ 8,500,000
Adjustments to additional paid in capital related to issuance costs attributable to equity component	$ 3,700,000
Capped calls
Debt Instrument [Line Items]
Capped caps initial strike price (in dollars per share) | $ / shares	$ 75.23	$ 38.58	$ 75.23
Capped caps initial cap price (in dollars per share) | $ / shares	$ 105.58	$ 57.16	$ 105.58
Convertible Debt | 2024 Notes
Debt Instrument [Line Items]
Aggregate principal		$ 230,000,000.0
Debt instrument stated rate (percent)		0.75%
Aggregate principal from exercise in full of over-allotment options		$ 30,000,000.0
Proceeds from debt offering, net of debt issuance costs		221,400,000
Debt instrument, unit of principal for conversion		$ 1,000
Number of shares per convertible note | equity_instrument		25.9182
Convertible debt conversion price (in dollars per share) | $ / shares		$ 38.58
Percentage of principal amount paid if repurchase due to fundamental change (percent)		100.00%
Threshold trading days in consideration of note conversion | day		20
Threshold consecutive trading days in analysis of conversion price | day		30
Threshold percentage of stock price if converted		130.00%
Threshold for five day period, product of sale price of common stock and conversion rate of notes		98.00%
Remaining amortization period for debt discount and debt issuance costs			3 years 2 months 12 days
Effective interest rate (percent)			4.66%
Convertible Debt | 2026 Notes
Debt Instrument [Line Items]
Aggregate principal	$ 517,500,000		$ 517,500,000
Aggregate principal from exercise in full of over-allotment options	67,500,000		67,500,000
Proceeds from debt offering, net of debt issuance costs	505,300,000
Debt instrument, unit of principal for conversion	$ 1,000		$ 1,000
Number of shares per convertible note | equity_instrument	13.2933
Convertible debt conversion price (in dollars per share) | $ / shares	$ 75.23		$ 75.23
Percentage of principal amount paid if repurchase due to fundamental change (percent)	100.00%
Threshold trading days in consideration of note conversion | day	20
Threshold consecutive trading days in analysis of conversion price | day	30
Threshold percentage of stock price if converted	130.00%
Threshold for five day period, product of sale price of common stock and conversion rate of notes	98.00%
Remaining amortization period for debt discount and debt issuance costs			5 years 10 months 24 days
Effective interest rate (percent)			6.61%
Other expense, ent
Debt Instrument [Line Items]
Interest expense			$ 14,600,000