Net loss per common share (Tables)

12 Months Ended

Dec. 31, 2015

Potential Dilutive Securities Outstanding

Potentially dilutive securities outstanding are summarized as follows (in shares):

	December 31,
	2015		2014		2013
Exercise of common stock options		19,779,229		21,541,664		24,237,940
Conversion of senior convertible notes into common stock		4,072,809		17,323,080		25,415,366
Exercise of common stock warrants		4,074,596		9,987,876		19,706,240
Vesting of restricted stock units		1,804,620		2,610,720		9,115,821
		29,731,254		51,463,340		78,475,367