Stock compensation (Tables)

3 Months Ended

Mar. 31, 2018

Stock compensation

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

	Employee Stock Options For the Three Months Ended				Employee Stock Purchase Plan For the Three Months Ended
	March 31,				March 31,
	2018		2017		2018		2017
Average risk-free interest rates	2.42	%	1.82	%	2.26	%	1.27	%
Average expected life (in years)	5.53		5.36		0.25		0.25
Volatility	45	%	49	%	36	%	40	%
Weighted-average fair value (in dollars)	41.59		51.93		18.17		17.82

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, 2017	3,909,701	11,206,553	$	68.36
Options granted	(1,308,438)	1,308,438	$	94.59
Options exercised	—	(486,605)	$	22.17
Options cancelled	139,853	(139,853)	$	102.47
Balance at March 31, 2018	2,741,116	11,888,533	$	72.74

Schedule of RSU award activity under the 2010 Stock Plan

		Shares Subject to
	Shares Available	Outstanding Awards
	for Grant	Shares	Grant Date Value
Balance at December 31, 2017	769,202	1,178,660	$	98.88
RSUs granted	(92,290)	92,290	$	93.62
RSUs cancelled	27,982	(27,982)	$	104.64
RSUs released	—	(160,123)	$	78.41
Balance at March 31, 2018	704,894	1,082,845	$	101.31

Schedule of summary of share activity

	Shares Issued
	and Outstanding
Balance at December 31, 2017	211,262,906
Exercise of stock options and issuance under ESPP	487,637
Settlement of employee restricted stock units	137,104
Conversion of convertible senior notes	539
Balance at March 31, 2018	211,888,186