Stock compensation (Tables)

6 Months Ended

Jun. 30, 2017

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 Six Months Ended				For the Three Months Ended				For the Six Months Ended
	June 30,								June 30,
	2017		2016		2017		2016		2017		2016		2017		2016
Average risk-free interest rates	1.56	%	1.20	%	1.79	%	1.47	%	1.38	%	0.58	%	1.31	%	0.71	%
Average expected life (in years)	5.41		5.08		5.36		5.01		0.50		0.50		0.50		0.50
Volatility	50	%	51	%	49	%	50	%	42	%	45	%	42	%	54	%
Weighted-average fair value (in dollars)	60.44		36.27		52.87		40.90		17.55		16.33		18.80		18.45

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, 2016	6,327,138	11,504,572	$	48.40
Options granted	(1,653,785)	1,653,785	$	116.29
Options exercised	—	(2,163,830)	$	29.74
Options cancelled	90,745	(90,745)	$	94.63
Balance at June 30, 2017	4,764,098	10,903,782	$	62.02

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, 2016	1,146,152	1,246,570		—
RSUs granted	(92,732)	92,732	$	120.36
RSUs cancelled	29,459	(29,459)	$	85.80
RSUs released	—	(284,903)	$	119.64
PSUs released	—	(43,376)	$	122.29
Balance at June 30, 2017	1,082,879	981,564		—