Stock compensation (Tables)

9 Months Ended

Sep. 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 Nine Months Ended				For the Three Months Ended				For the Nine Months Ended
	September 30,								September 30,
	2017		2016		2017		2016		2017		2016		2017		2016
Average risk-free interest rates	1.81	%	1.05	%	1.79	%	1.31	%	1.47	%	0.77	%	1.37	%	0.77	%
Average expected life (in years)	4.99		4.96		5.24		4.99		0.50		0.50		0.50		0.50
Volatility	48	%	50	%	49	%	50	%	39	%	38	%	41	%	48	%
Weighted-average fair value (in dollars)	55.80		36.66		53.81		39.29		20.46		18.33		19.89		18.94

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	(2,437,233)	2,437,233	$	120.15
Options exercised	—	(2,546,517)	$	30.68
Options cancelled	116,586	(116,586)	$	96.30
Balance at September 30, 2017	4,006,491	11,278,702	$	67.41

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	$	82.05
RSUs granted	(396,331)	396,331	$	126.45
RSUs cancelled	41,376	(41,376)	$	89.68
RSUs released	—	(382,133)	$	127.72
PSUs released	—	(43,376)	$	122.29
Balance at September 30, 2017	791,197	1,176,016	$	100.86

Schedule of summary of share activity

The following table summarizes our share activity:

	Shares Issued
	and Outstanding
Balance at December 31, 2016	188,848,752
Exercise of stock options and issuance under ESPP	2,643,324
Settlement of employee restricted stock units and performance shares	285,958
Conversion of convertible senior notes	14,296,332
Public issuance of common stock	4,945,000
Balance at September 30, 2017	211,019,366