Stock Compensation Plans and Stock Based Compensation (Details 6) (Restricted Stock [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Y
Restricted Stock [Member]
Summary of changes in restricted stock awards outstanding under Cadence's equity incentive plans
Unvested shares as of January 1, 2011	8,297
Granted	4,416
Vested	(4,335)
Forfeited	(551)
Unvested shares as of December 31, 2011	7,827
Unvested shares expected to vest as of December 31, 2011	7,391
Unvested shares as of January 1,, 2011, Weighted-Average Grant Date Fair Value	$ 6.64
Granted, Weighted-Average Grant date Fair Value	$ 9.83
Vested, Weighted-Average Grant Date Fair Value	$ 6.64
Forfeited, Weighted-Average Grant Date Fair Value	$ 7.33
Unvested shares as of December 31, 2011, Weighted-Average Grant Date Fair Value	$ 8.39
Unvested shares expected to vest as of December 31, 2011, Weighted-Average Grant Date Fair Value	$ 8.37
Unvested shares as of January 1, 2011, Weighted-Average Remaining Vesting Terms	1.7
Unvested shares as of December 31, 2011, Weighted-Average Remaining Vesting Terms	1.7
Unvested shares expected to vest as of December 31, 2011, Weighted-Average Remaining Vesting Terms	1.7
Unvested shares as of January 1, 2011, Aggregate Intrinsic Value	$ 68,532
Unvested shares as of December 31, 2011, Aggregate Intrinsic Value	81,405
Unvested shares expected to vest as of December 31, 2011, Aggregate Intrinsic Value	$ 76,859