Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2013

Stockholders' Equity Note [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	(244,054	)	244,054		134.56
Exercised	—		(556,819	)	70.30
Balances as of March 31, 2013	3,804,983		4,260,187		75.09		6.72	$	502,450
Vested and exercisable at March 31, 2013			4,260,187		75.09		6.72	$	502,450

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
	March 31, 2013		March 31, 2012
Dividend yield	—	%	—	%
Expected volatility	54	%	65	%
Risk-free interest rate	1.87	%	1.97	%
Suboptimal exercise factor	2.33 - 3.59		2.26 - 3.65