Debt - Summary of Convertible Debt (Detail) $ / shares in Units, $ in Thousands	Oct. 15, 2020 USD ($) d $ / shares shares	Sep. 30, 2020 USD ($)	May 31, 2020 USD ($) $ / shares	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Convertible Notes		$ 1,500,000
Convertible Notes, net of unamortized discount and deferred offering costs		1,074,164		$ 486,238	[1]
Short-term convertible debt, net		374,290		361,882	[1]
Total convertible debt, net		1,448,454		848,120
Total fair value of fixed rate convertible debt		$ 1,482,737		$ 927,518
1.25% Senior Subordinated Convertible Notes Due in May 2027
Debt Instrument [Line Items]
Convertible notes stated rate		1.25%		1.25%
Convertible Notes		$ 600,000		$ 0
Convertible debt, unamortized discount		(12,792)		0
Convertible debt, Unamortized deferred offering costs		(709)		0
Convertible Notes, net of unamortized discount and deferred offering costs		586,499		0
Total fair value of fixed rate convertible debt		$ 590,010		$ 0
1.25% Senior Subordinated Convertible Notes Due in May 2027 | Senior Subordinated Notes
Debt Instrument [Line Items]
Convertible notes stated rate			1.25%
Convertible debt, unamortized discount			$ (13,500)
Debt instrument, convertible, conversion price, per share (in dollars per share) | $ / shares			$ 137.47
0.599% Senior Subordinated Convertible Notes Due in August 2024
Debt Instrument [Line Items]
Convertible notes stated rate		0.599%		0.599%
Convertible Notes		$ 495,000		$ 495,000
Convertible debt, unamortized discount		(5,470)		(6,533)
Convertible debt, Unamortized deferred offering costs		(1,865)		(2,229)
Convertible Notes, net of unamortized discount and deferred offering costs		487,665		486,238
Total fair value of fixed rate convertible debt		$ 517,730		$ 521,839
1.50% Senior Subordinated Convertible Notes Due in October 2020
Debt Instrument [Line Items]
Convertible notes stated rate		1.50%		1.50%
Convertible Notes		$ 374,993		$ 374,993
Convertible debt, unamortized discount		(649)		(12,078)
Convertible debt, Unamortized deferred offering costs		(54)		(1,033)
Short-term convertible debt, net		374,290		361,882
Total fair value of fixed rate convertible debt		$ 374,997		$ 405,679
1.50% Senior Subordinated Convertible Notes Due in October 2020 | Subsequent Event
Debt Instrument [Line Items]
Repayments of convertible debt	$ 375,000
Shares issued (in shares) | shares	0
Measurement period | d	25
1.50% Senior Subordinated Convertible Notes Due in October 2020 | Subsequent Event | Senior Subordinated Notes
Debt Instrument [Line Items]
Debt instrument, convertible, conversion price, per share (in dollars per share) | $ / shares	$ 94.15

[1] December 31, 2019 balances were derived from the audited Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019, filed with the SEC on February 27, 2020.