Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2015

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, 2014	2,860,744		3,263,631		$	151.53
Granted	(148,156	)	148,156		417.43
Exercised			(204,880	)	50.12
Balances as of March 31, 2015	2,712,588		3,206,907		$	170.29	6.30	$	801,626
Vested and exercisable as of March 31, 2015			3,206,907		$	170.29	6.30	$	801,626

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 and the valuation data:

	Three Months Ended
	March 31, 2015			March 31, 2014
Dividend yield	—		%	—		%
Expected volatility	36		%	48		%
Risk-free interest rate	2.03		%	2.83		%
Suboptimal exercise factor	2.48			2.66 - 4.07
Valuation data:
Weighted-average fair value (per share)	$	185.22		$	221.79
Total stock-based compensation expense (in thousands)	$	27,441		$	25,825
Total income tax benefit related to stock options (in thousands)	$	10,392		$	9,899