CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Issuance of shares of Common Stock upon exercise of stock options and restricted stock units	3,012,937	2,068,226	5,220,474
Issuance of shares of Common Stock under the ESPP	157,277	126,648	194,453
Issuance of shares of Common Stock for services rendered	2,532	3,438	2,017
Issuance of shares of Common Stock	4,945,000
4.75% Convertible Senior Notes Due 2015
Issuance of shares of Common Stock upon conversion of convertible senior notes			10,352,784
Convertible Senior Notes 1.25 Percent Due 2020
Issuance of shares of Common Stock upon conversion of convertible senior notes	7,095,350	77	3,902
Convertible Senior Notes 0.375 Percent Due 2018
Issuance of shares of Common Stock upon conversion of convertible senior notes	7,201,058	114