Convertible Senior Notes and Capped Call Transactions - Narrative (Details)		6 Months Ended
	May 11, 2020 USD ($) $ / shares	Jun. 30, 2020 USD ($) tradingDay $ / shares	Jun. 30, 2019 USD ($)	Dec. 31, 2019 $ / shares
Debt Instrument [Line Items]
Proceeds from issuance of convertible senior notes, net of issuance costs		$ 245,308,000	$ 0
Purchases of capped calls		$ 29,348,000	$ 0
Common stock, par value (in dollars per share) | $ / shares		$ 0.001		$ 0.001
Cap price | $ / shares		$ 141.72
Percentage premium over the last reported sale price of company common stock used to calculate cap price		100.00%
2025 Senior Notes
Debt Instrument [Line Items]
Principal amount including additional purchases from exercised options		$ 253,000,000
Equity component, net of discount and issuance costs		30,794,000
Fair value of the notes		$ 294,001,000
Convertible Debt
Debt Instrument [Line Items]
Purchases of capped calls	$ 29,348,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.001
Convertible Debt | 2025 Senior Notes
Debt Instrument [Line Items]
Principal amount including additional purchases from exercised options	$ 253,000,000
Interest rate, stated percentage	1.25%
Principal amount	$ 220,000,000
Additional amount included in principal from exercised options	33,000,000
Proceeds from issuance of convertible senior notes, net of issuance costs	$ 245,158,000
Debt instrument, convertible, conversion ratio		10.8556
Initial conversion price (in dollars per share) | $ / shares		$ 92.12
Repurchase of notes percentage		100.00%
Interest rate, effective percentage		4.51%
Equity component, net of discount and issuance costs		$ 31,779,000
Debt issuance costs of liability component		6,857,000
Convertible Debt | 2025 Senior Notes | Additional paid-in capital
Debt Instrument [Line Items]
Debt issuance costs of equity component		$ 985,000
Convertible Debt | 2025 Senior Notes | Debt Conversion, Option One
Debt Instrument [Line Items]
Threshold trading days (in trading days) | tradingDay		20
Threshold consecutive trading days | tradingDay		30
Threshold percentage of conversion price		130.00%
Convertible Debt | 2025 Senior Notes | Debt Conversion, Option Two
Debt Instrument [Line Items]
Threshold consecutive trading days | tradingDay		5
Threshold percentage of conversion price		98.00%
Threshold consecutive business days | tradingDay		5