Summary of Significant Accounting Policies - Share Repurchases (Details) - USD ($) $ in Thousands		12 Months Ended
	Jun. 02, 2016	Dec. 31, 2019	Dec. 31, 2018
Equity, Class of Treasury Stock [Line Items]
Repurchases of shares of common stock, in shares		0	1,937,844
Repurchases of shares of common stock		$ 0	$ 25,048
June 2018 Program
Equity, Class of Treasury Stock [Line Items]
Repurchases of shares of common stock		0	0
January 2019 Program
Equity, Class of Treasury Stock [Line Items]
Repurchases of shares of common stock		0
December 2017 Program
Equity, Class of Treasury Stock [Line Items]
Repurchases of shares of common stock			25,048
Convertible Senior Notes | 2019 Convertible Notes
Equity, Class of Treasury Stock [Line Items]
Convertible Notes Repurchases, Principal Amount		0	6,311
Convertible Notes Repurchases		0	6,689
Convertible Senior Notes | 2019 Convertible Notes | June 2018 Program
Equity, Class of Treasury Stock [Line Items]
Convertible Notes Repurchases		0	0
Convertible Senior Notes | 2019 Convertible Notes | January 2019 Program
Equity, Class of Treasury Stock [Line Items]
Convertible Notes Repurchases		0
Convertible Senior Notes | 2019 Convertible Notes | December 2017 Program
Equity, Class of Treasury Stock [Line Items]
Convertible Notes Repurchases			6,689
Convertible Senior Notes | 2036 Convertible Notes
Equity, Class of Treasury Stock [Line Items]
Convertible Notes Repurchases, Principal Amount		6,673	55,700
Convertible Notes Repurchases	$ 147,118	14,638	110,828
Convertible Senior Notes | 2036 Convertible Notes | June 2018 Program
Equity, Class of Treasury Stock [Line Items]
Convertible Notes Repurchases		7,435	67,565
Convertible Senior Notes | 2036 Convertible Notes | January 2019 Program
Equity, Class of Treasury Stock [Line Items]
Convertible Notes Repurchases		$ 7,203
Convertible Senior Notes | 2036 Convertible Notes | December 2017 Program
Equity, Class of Treasury Stock [Line Items]
Convertible Notes Repurchases			$ 43,263