Stock incentive plan (Tables)

12 Months Ended

Dec. 31, 2013

Stock incentive plan

Summary of stock option activity

	Number of options			Weighted- average exercise price		Weighted- average remaining contractual life (in years)		Aggregate intrinsic value
Outstanding as of December 31, 2012		8,052,473		$	2.34		5.46	$	9,221,448
Options granted		949,300
Options exercised		(540,879	)
Options cancelled		(65,666	)
Options forfeited		(157,345	)
Outstanding as of December 31, 2013		8,237,883		$	2.38		5.62		3,766,674
Options exercisable as of December 31, 2013		6,774,584			2.31		4.92		3,565,363
Vested and expected to vest as of December 31, 2013		8,190,603			2.38		5.60		3,761,252

Schedule of additional information pertaining to the stock options

	Year ended December 31,
	2013		2012		2011
Weighted-average grant date fair value for options granted during the period	$	1.14	$	1.20	$	0.70
Total fair value of options vested during the period		949,588		1,126,087		549,802
Total intrinsic value of options exercised during the period		212,580		360,371		348,153

Summary of the status of the non-vested shares of restricted stock grants

	Number of Awards			Weighted Average Grant Date Fair Value
Non-vested awards as of January 1, 2013		915,000		$	1.97
Awards granted		875,583			2.22
Awards vested		(16,250	)		2.92
Awards cancelled and forfeited		(9,000	)		2.92
Non-vested awards as of December 31, 2013		1,765,333		$	2.08