Net loss per common share (Tables)

12 Months Ended

Dec. 31, 2012

Potential Dilutive Securities Outstanding

Potentially dilutive securities outstanding are summarized as follows:

	December 31,
	2010		2011		2012
Exercise of common stock options		7,760,833		10,082,351		18,674,539
Conversion of senior convertible notes into common stock		19,826,113		19,826,113		19,826,113
Exercise of common stock warrants		—		—		86,062,440
Vesting of restricted stock units		3,271,644		4,140,388		3,761,031
		30,858,590		34,048,852		128,324,123