Stock Option And Grant Plan (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for grant under the plan	30,400,000
Percentage of voting interest to be held by optionee	10.00%
Exercise price as a percentage of fair value at the time of grant	110.00%
Expiration period of options from the date of grant	10 years
Expiration period for optionee who meets the 10% criteria	5 years
Duration of offering the purchase plan	4 years
Maximum months after sale event where awards fully vest when service relationship terminated without cause	18 months
Maximum number of days that may be granted to terminated employee to exercise awards prior to termination	15 days
Total estimated grant date fair values of stock options vested during period	$ 23,300,000	$ 20,200,000	$ 16,700,000
Total unrecognized estimated compensation cost	61,900,000
Weighted average period of recognition of unrecognized compensation cost (years)	2 years
Total intrinsic value of options exercised during the period	64,700,000	42,600,000	88,000,000
Unvested options	3,000,000
Aggregate intrinsic value of unvested options	37,900,000
Weighted average exercise price of unvested options	$ 54.94
Weighted average remaining contractual term of unvested stock options (years)	8 years 6 months
Cash received from the exercise of stock options	31,960,000	22,791,000	22,929,000
Tax benefit from exercise of stock options	18,600,000
Excess tax benefit from exercise of stock options	13,888,000	10,046,000	11,753,000
Business acquisition performance equity awards service period	3 years
Deferred Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred stock units earned with underlying shares remaining unissued until the service termination	95,227
Deferred stock units earned during the period	28,523
Performance Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance-based restricted stock units granted	100,000	92,500	80,500
Measurement period of restricted stock units	3 years
Value of the restricted stock units on the grant date	$ 33.16	$ 32.05	$ 25.00
Number of shares available for offerings under purchase plan	76,500
Stock-based compensation expense	2,600,000	1,600,000	590,000
Compensation expense expected to be recorded in 2013	2,200,000
Compensation expense expected to be recorded in 2014	1,200,000
Apache Design Solutions, Inc.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Business acquisition, potential performance equity awards	$ 13,000,000