Stock compensation (Tables)

3 Months Ended

Mar. 31, 2016

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 For the Three Months Ended				Employee Stock Purchase Plan For the Three Months Ended
	March 31,				March 31,
	2016		2015		2016		2015
Average risk-free interest rates	1.50	%	1.35	%	0.73	%	0.56	%
Average expected life (in years)	5.00		5.05		0.25		0.25
Volatility	49	%	50	%	61	%	38	%
Weighted-average fair value (in dollars)	41.56		32.59		26.67		9.56

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, 2015	3,846,717	11,052,279	$	33.55
Options granted	(1,412,583)	1,412,583	$	94.69
Options exercised	—	(751,784)	$	14.06
Options cancelled	68,324	(68,324)	$	73.24
Options expired	—	(1,834)	$	3.11
Balance at March 31, 2016	2,502,458	11,642,920	$	42.00

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, 2015	834,433	565,567		—
RSUs granted	(216,711)	216,711	$	88.28
PSUs granted	—	—		—
RSUs cancelled	12,843	(12,843)	$	67.62
PSUs cancelled	—	—		—
Balance at March 31, 2016	630,565	769,435		—