CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) (USD $)	Mar. 31, 2014	Dec. 31, 2013
LIABILITIES AND STOCKHOLDERS' EQUITY
Interest rate on convertible senior notes (in hundredths)	2.75%	2.75%
Stockholders' equity:
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	117,541,860	116,471,371
Common stock, shares outstanding (in shares)	117,541,860	116,471,371