Stock compensation (Tables)

6 Months Ended

Jun. 30, 2015

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,
	2015		2014		2015		2014		2015		2014		2015		2014
Average risk-free interest rates	1.38	%	1.32	%	1.35	%	1.20	%	0.64	%	0.47	%	0.60	%	0.52	%
Average expected life (in years)	5.20		5.01		5.06		4.55		0.50		0.50		0.50		0.50
Volatility	49	%	52	%	50	%	50	%	27	%	42	%	36	%	52	%
Weighted-average fair value (in dollars)	45.56		22.69		33.80		25.95		9.24		7.87		9.90		9.13

Schedule of option activity under the 2010 Stock Plan

			Shares Subject to Outstanding Options
	Shares Available for Grant		Shares		Weighted Average Exercise Price
Balance at December 31, 2014	5,399,816		14,655,043		$	21.96
Options granted	(1,789,638	)	1,789,638		$	76.79
Options exercised	—		(3,801,201	)	$	16.18
Options cancelled	278,099		(278,099	)	$	42.92
Balance at June 30, 2015	3,888,277		12,365,381		$	31.20

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, 2014	1,001,523		398,477		—
RSUs granted	(188,095	)	188,095		$	75.88
PSUs granted	—		—		—
RSUs cancelled	25,278		(25,278	)	$	61.40
PSUs cancelled	4,958		(4,958	)	$	64.55
Balance at June 30, 2015	843,664		556,336		—