CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares	Jun. 30, 2015	Dec. 31, 2014
Stockholders' equity:
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	119,881,615	118,442,726
Common stock, shares outstanding (in shares)	119,881,615	118,442,726
1 Percent Convertible Senior Notes [Member]
LIABILITIES AND STOCKHOLDERS' EQUITY
Interest rate on convertible senior notes	1.00%	1.00%
2 3/4 Percent Convertible Senior Notes [Member]
LIABILITIES AND STOCKHOLDERS' EQUITY
Interest rate on convertible senior notes	2.75%	2.75%