Stock compensation (Tables)

9 Months Ended

Sep. 30, 2015

Stock compensation

Schedule of valuation assumptions used for valuation of fair value of stock compensation granted

We utilized the Black-Scholes valuation model for estimating the fair value of the stock compensation granted, with the following weighted-average assumptions:

		Employee Stock Options								Employee Stock Purchase Plan
		For the Three Months Ended				For the Nine Months Ended				For the Three Months Ended				For the Nine Months Ended
		September 30,								September 30,
		2015		2014		2015		2014		2015		2014		2015		2014
Average risk-free interest rates		1.22	%	1.30	%	1.35	%	1.21	%	0.64	%	0.56	%	0.64	%	0.56	%
Average expected life (in years)		4.44		4.50		5.04		4.54		0.50		0.50		0.50		0.50
Volatility		47	%	51	%	50	%	51	%	51	%	48	%	51	%	48	%
Weighted-average fair value (in dollars)		46.08		21.82		34.29		25.56		13.45		9.36		13.45		9.36

Schedule of option activity under the 2010 Stock Plan

Option activity under the 2010 Stock Plan was as follows:

		Shares Subject to
		Outstanding Options
	Shares Available		Weighted Average
	for Grant	Shares	Exercise Price
Balance at December 31, 2014	5,399,816	14,655,043	$	21.96
Options granted	(1,864,485)	1,864,485	$	78.40
Options exercised	—	(4,574,951)	$	16.51
Options cancelled	318,876	(318,876)	$	44.38
Balance at September 30, 2015	3,854,207	11,625,701	$	32.55

Schedule of RSU and PSU award activity under the 2010 Stock Plan

RSU and PSU award activity under the 2010 Stock Plan was as follows:

		Shares Subject to
	Shares Available	Outstanding Awards
	for Grant	Shares	Grant Date Value
Balance at December 31, 2014	1,001,523	398,477		—
RSUs granted	(197,916)	197,916	$	77.91
PSUs granted	—	—		—
RSUs cancelled	29,671	(29,671)	$	62.29
PSUs cancelled	4,958	(4,958)	$	64.55
Balance at September 30, 2015	838,236	561,764		—