Stockholders' Equity - Additional Information (Details) $ / shares in Units, shares in Millions			1 Months Ended	12 Months Ended
	Jan. 23, 2018 shares	May 25, 2017 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($) vote	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) shares	Sep. 30, 2020 USD ($)
Class of Stock [Line Items]
Premiums for capped call options			$ 32,900,000		$ 32,890,000
Proceeds from sale of common stock				$ 0	0	$ 135,972,000
Number of voting rights | vote				1
Common Stock
Class of Stock [Line Items]
Proceeds from sale of common stock		$ 72,700,000				$ 136,400,000	$ 61,100,000
New shares issued under shelf registration (in shares) | shares	1.3	1.4
Common stock issued and sold under sales agreement (in shares) | shares							1.1
Price per share issued under underwriting agreement (in dollars per share) | $ / shares		$ 53.75
Convertible Senior Notes Due 2024 | Convertible debt
Class of Stock [Line Items]
Principal amount			316,250,000	$ 316,250,000	$ 316,250,000
Equity component of convertible debt			$ 128,400,000					$ 128,400,000