Stock incentive plan (Tables)

12 Months Ended

Dec. 31, 2014

Stock-based compensation expense and assumptions

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, 2013		8,237,883		$	2.38		5.62	$	3,766,674
Options granted		576,700			3.18
Options exercised		(688,760	)		2.03
Options cancelled		(321,520	)		2.59
Options expired		(402,903	)		2.50
Options forfeited		(334,524	)		2.85
Outstanding as of December 31, 2014		7,066,876		$	2.44		5.22		885,057
Options exercisable as of December 31, 2014		6,092,256			2.36		4.65		884,337
Vested and expected to vest as of December 31, 2014		7,028,232			2.44		5.20		885,021

Schedule of additional information pertaining to the stock options

	Year ended December 31,
	2014		2013		2012
Weighted-average grant date fair value for options granted during the period	$	1.36	$	1.14	$	1.20
Total fair value of options vested during the period		775,899		949,588		1,126,087
Total intrinsic value of options exercised during the period		803,141		212,580		360,371

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, 2014		1,765,333		$	2.08
Awards granted		930,830			0.60
Awards vested		(132,902	)		2.79
Awards repurchased		(320,250	)		1.97
Awards cancelled and forfeited		(601,426	)		2.29
Non-vested awards as of December 31, 2014		1,641,585			1.13