Employee benefit plans (Tables)

12 Months Ended

Dec. 31, 2018

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

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

The fair value of stock options granted was estimated as of the grant date using the following assumptions:

	Year ended December 31,
	2018	2017	2016
Volatility	51%	44%-49%	44%-45%
Expected term (years)	5.4-6.1	5.3-5.8	5.2-6.1
Risk-free interest rate	2.7%-3.0%	1.8%-2.1%	1.2%-2.0%
Dividend yield	—%	—%	—%

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block]

The fair value of stock purchase rights granted under the ESPP was estimated using the following assumptions:

	Year ended December 31,
	2018	2017	2016
Volatility	48%-53%	33%-36%	43%-54%
Expected term (years)	0.5	0.5	0.5
Risk-free interest rate	1.8%-2.2%	0.7%-1.2%	0.4%-0.5%
Dividend yield	—%	—%	—%

schedule of share-based compensation, Performance Stock Units Award Activity [Table Text Block]

A summary of the Company’s PSU activity is as follows:

	Shares (in thousands)		Weighted average grant date fair value
Non-vested shares at December 31, 2017	—		$	—
Granted	334		5.76
Vested	—		—
Forfeited	(34	)	5.74
Non-vested shares at December 31, 2018	300		$	5.76

Schedule of Share-based Compensation, Stock Options, Activity

A summary of the Company’s stock option activity is as follows:

	Shares (in thousands)		Weighted average exercise price		Weighted-average remaining contractual term (in years)	Aggregate intrinsic value (in thousands)
Outstanding at December 31, 2017	9,809		$	11.16	6.00	$	19,971
Granted	1,333		5.77
Exercised	(654	)	0.74
Forfeited/Cancelled	(4,495	)	16.26
Outstanding at December 31, 2018	5,993		$	7.28	5.44	$	7,897
Vested and expected to vest at December 31, 2018	5,988		$	7.28	5.44	$	7,897
Exercisable at December 31, 2018	4,459		$	7.40	4.20	$	7,897

Schedule of Share-based Compensation, Restricted Stock Units Award Activity

A summary of the Company’s RSU activity is as follows:

	Shares (in thousands)		Weighted average grant date fair value
Non-vested shares at December 31, 2017	9,483		$	11.87
Granted	4,612		5.83
Vested	(3,559	)	11.70
Forfeited	(3,319	)	11.75
Non-vested shares at December 31, 2018	7,217		$	8.15

Allocation of Stock-based Compensation Expense

The following table summarizes stock-based compensation expense included in the consolidated statements of operations:

	Year ended December 31,
(in thousands)	2018		2017		2016
Cost of revenue	$	1,954	$	1,935	$	1,616
Research and development	19,636		24,963		31,365
Sales and marketing	9,459		10,498		13,883
General and administrative	9,838		13,859		22,663
Total stock-based compensation expense	$	40,887	$	51,255	$	69,527