Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2013

Stockholders' Equity and Stock-based Compensation Disclosure [Abstract]

Summary Of Activity Related To Stock Option Plans

A summary of the activities related to the Company’s stock option plans is as follows:

			Options Outstanding
	Shares Available for Grant		Number of Shares		Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (in Years)	Aggregate Intrinsic Value (in Thousands)
Balances as of December 31, 2012	4,049,037		4,572,952		$	71.33
Granted	(406,292	)	406,292		162.52
Exercised			(1,004,266	)	67.70
Balances as of June 30, 2013	3,642,745		3,974,978		81.57		6.49	$	524,708
Vested and exercisable at June 30, 2013			3,974,978		81.57		6.49	$	524,708

Summary Of Assumptions Used To Value Stock Option Grants Using Lattice-Binomial Model

The following table summarizes the assumptions used to value stock option grants using the lattice-binomial model:

	Three Months Ended				Six Months Ended
	June 30, 2013		June 30, 2012		June 30, 2013		June 30, 2012
Dividend yield	—	%	—	%	—	%	—	%
Expected volatility	53	%	61	%	53% - 54%		61% - 65%
Risk-free interest rate	1.88	%	2.01	%	1.87% - 1.88%		1.97% - 2.01%
Suboptimal exercise factor	2.39 - 3.61		2.26 - 3.65		2.33 - 3.61		2.26 - 3.65