Stockholders' Equity - Stock Reserved for Future Issuance (Details) shares in Thousands	Dec. 31, 2016 shares
Common stock options:
Shares reserved for future issuance	76,393
Stock Options [Member]
Common stock options:
Shares reserved for future issuance	410
Restricted Stock Units And Performance-Based Restricted Stock Units [Member]
Common stock options:
Shares reserved for future issuance	2,150
Available for Future Grant [Member]
Common stock options:
Shares reserved for future issuance	4,383
ESPP [Member]
Common stock options:
Shares reserved for future issuance	1,398
2.75% Senior Convertible Notes due 2017 [Member]
Common stock options:
Shares reserved for future issuance	1,954
2.25% Senior Convertible Notes due 2021 [Member]
Common stock options:
Shares reserved for future issuance	14,396
Senior Convertible Warrants Due 2017 [Member]
Common stock options:
Shares reserved for future issuance	19,106
Senior Convertible Warrants Due 2021 [Member]
Common stock options:
Shares reserved for future issuance	32,596