Stock compensation (Tables)

9 Months Ended

Sep. 30, 2016

Stock compensation

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

		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,
		2016		2015		2016		2015		2016		2015		2016		2015
Average risk-free interest rates		1.05	%	1.22	%	1.31	%	1.35	%	0.77	%	0.64	%	0.77	%	0.64	%
Average expected life (in years)		4.96		4.44		4.99		5.04		0.50		0.50		0.50		0.50
Volatility		50	%	47	%	50	%	50	%	38	%	51	%	48	%	51	%
Weighted-average fair value (in dollars)		36.66		46.08		39.29		34.29		18.33		13.45		18.94		13.45

Schedule of option activity under the 2010 Stock Plan

		Shares Subject to
		Outstanding Options
	Shares Available		Weighted Average
	for Grant	Shares	Exercise Price
Balance at December 31, 2015	3,846,717	11,052,279	$	33.55
Additional authorization	5,000,000	—		—
Options granted	(2,606,079)	2,606,079	$	89.53
Options exercised	—	(1,524,934)	$	19.16
Options cancelled	164,542	(156,555)	$	77.13
Options expired	(1,834)	(7,987)	$	39.67
Balance at September 30, 2016	6,403,346	11,968,882	$	46.99

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

		Shares Subject to
	Shares Available	Outstanding Awards
	for Grant	Shares	Grant Date Value
Balance at December 31, 2015	834,433	565,567		—
Additional authorization	1,000,000	—		—
RSUs granted	(708,426)	708,426	$	85.28
RSUs cancelled	32,880	(32,880)	$	73.38
PSUs cancelled	1,948	(1,948)	$	64.55
RSUs released	—	(7,278)	$	78.49
Balance at September 30, 2016	1,160,835	1,231,887		—