Common stock (Tables)

12 Months Ended

Dec. 31, 2013

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Reserved Shares for Issuance

At December 31, 2013, the Company has reserved shares for issuance of common stock as follows:

	Common Shares
Reserved under stock option plans	328,519
Exercise of warrants to purchase common stock	44,491
Total reserved for issuance	373,010

Schedule of Stock Option Activity

The following table summarizes the combined stock option activity under the 2000 Plan, the 2006 Plan and the 2012 Plan and non-plan stock option agreements:

	Options outstanding
	Number of options		Weighted average exercise price		Weighted average remaining contractual term	Aggregate intrinsic value
					(in years)	(in thousands)
Outstanding at December 31, 2012	3,187,559		$	7.51	6.81	$	56,362
Options granted	675,460		16.85
Options exercised	(420,492	)	3.94
Options canceled	(142,102	)	12.17
Options expired	(13,221	)	22.47
Outstanding at December 31, 2013	3,287,204		$	9.62	6.45	$	24,880
Options vested and expected to vest as of December 31, 2013	3,238,937		$	9.51	6.41	$	24,824
Options vested and exercisable as of December 31, 2013	1,996,061		$	5.82	5.05	$	21,169

Options, Grants in Period, Wtd Avg Grant Date Fair Value

Using the Black-Scholes option-pricing model, the weighted-average grant-date fair value of options granted to employees during the years ended December 31, 2013, 2012 and 2011 was $7.34 per share, $10.19 per share, and $3.30 per share, respectively. Further information regarding the value of employee options vested and exercised during the years ended December 31, 2013, 2012 and 2011 is set forth below.

	Years ended December 31,
(in thousands)	2013		2012		2011
Grant-date fair value of options vested during period	$	3,053	$	2,256	$	881
Intrinsic value of options exercised during period	5,896		24,846		2,565

Schedule of Valuation Assumptions for Stock Options

The Company uses the Black-Scholes option-pricing model to calculate the fair value of stock options on their grant date. This model requires the following major inputs: the estimated fair value of the underlying common stock, the expected term of the option, the expected volatility of the underlying common stock over the expected life of the option, the risk-free interest rate and expected dividend yield. The following assumptions were used for each respective period for employee stock-based compensation:

	Years ended December 31,
	2013	2012	2011
Expected Term (in years)	5.38 - 5.43	5.23 - 5.60	5.49 - 5.73
Volatility	46.7% - 48.1%	47.9% - 48.7%	44.7% - 47.6%
Risk-free interest rate	0.81% - 1.80%	0.72% - 1.03%	0.98% - 2.48%
Dividend yield	0.0%	0.0%	0.0%

Schedule of Valuation Assumptions for ESPP

The Company uses the Black-Scholes option-pricing model to calculate the fair value of periodic ESPP offerings on their offer date. The following assumptions were used for each respective period for the ESPP:

	Years ended December 31,
	2013	2012
Expected Term (in years)	0.25 - 0.50	0.50 - 0.88
Volatility	33.3% - 36.0%	43.2% - 50.0%
Risk-free interest rate	0.05% - 0.13%	0.14% - 0.18%
Dividend yield	0.0%	0.0%

Summary of the restricted stock activty

A summary of the restricted stock activity for the year ended December 31, 2013 is presented below:

	Restricted Stock Awards				Restricted Stock Units
	Number of shares		Weighted Average Grant Date Fair Value per Share		Number of shares		Weighted Average Grant Date Fair Value per Share
Outstanding at December 31, 2012	24,152		$	12.42	373,908		$	25.34
Granted	—		—		558,686		16.91
Vested	(12,076	)	12.42		(117,245	)	25.18
Forfeited	—		—		(60,078	)	23.63
Outstanding at December 31, 2013	12,076		$	12.42	755,271		$	19.24

Schedule of Share-based Comp for Nonemployee Services

The fair value of the stock options granted to non-employees was calculated using the Black-Scholes option-pricing model with the following assumptions:

	As of December 31,
		2012	2011
Expected Term (in years)		8.67	8.83 - 10.0
Volatility		46.7%	45.0% - 54.0%
Risk-free interest rate		1.77%	1.63% - 3.41%
Dividend yield		0.0%	0.0%

Schedule of Share-based Comp Allocation of Period Costs

The following table presents the stock-based compensation allocation of expense (both for employees and non-employees):

	Years ended December 31,
(in thousands)	2013		2012		2011
Cost of revenue	$	967	$	421	$	30
Research and development	861		449		121
Sales and marketing	2,942		1,262		285
General and administrative	3,897		2,100		1,022
Total stock-based compensation	$	8,667	$	4,232	$	1,458